In 4.19 John, Dean, and Sam made decisions that were well-intentioned by imperfect, that were driven by both pure and selfish emotions, and all wanted to do the right thing even though they disagreed on what that was exactly. In a season about Heaven and Hell, 4.19 was an episode that revealed just how human those Winchester boys are...
I need to begin this with a confession: I started watching this episode with a bad attitude that didn’t last very long. Oh, I had a million doubts and scornful thoughts: introducing some as-of-yet-unknown teenage brother? Please - it struck me as bad fan fiction more than anything else and while I was relatively sure that this kid wouldn’t end up a series regular or anything I was fully prepared to hate his guts. That lasted until partway through the first scene with Adam and I found myself actually liking this kid, this mix of early Sam (earnestness and shaken-but-not-broken innocence) and early Dean (strong devotion to family and mother angst). If the ghoul’s representation was even close to what the real Adam was like, Sam and Dean really missed out on by not being able to get to know him.
The most significant thing about Adam’s existence in terms of the show, however, is how John, Sam, and Dean all reacted to him and how those reactions tell a great deal about themselves and their relationships with each other. None of the Winchester boys are purely noble, nor are they driven completely by selfish impulses - it all boils down to that human mixture of both good and bad. The ways each of them chose to deal with Adam sudden presence in their lives came from both wanting to do the right thing and their own insecurities; and in the end all three of them turned out to be right and wrong at the same time.
John’s relationship with Adam is mostly conjecture, as all we know about it we got from a few photographs around the Milligan house and a ghoul who had no reason not to lie if it suited his mission. While I believe a fair amount of what the ghoul said was true, his ascertain that John and Adam had some sort of ongoing relationship was most likely an exaggeration to illicit sympathy from the boys when he thought they were just John’s friends and to cloud their judgment once he learned they were in fact his sons. In truth, it’s doubtful that John and Adam spent nearly as much time together as the ghoul told Sam and Dean. The timeline supports that: he found out about the kid and visited in 2004, the YED resurfaced in 2005, and his life became consumed with that hunt up to the point where he died in 2006. In all likelihood John visited Adam only once - when he found out he had a twelve-year-old son who wanted to meet him.
The call couldn’t have come at a more vulnerable time for John, at least in terms of him being a dad. By 2004 Sam was away at college and he hadn’t spoken to him in two years; Dean was 25, old enough to go on hunts by himself and not really needing his dad anymore. Adam must have felt like a second chance to be the father he would have been had Mary not died. The fishing, the baseball game - it must have been a cathartic experience for him, a way of proving to himself that he did have what it took to be a normal and loving father if the monsters were taken out of the equation. He probably did everything he could to give Adam as many happy memories of his father as possible.
Ultimately, however, John walked away and kept the fact that they had a half brother from Sam and Dean. A part of that was John trying to do the right thing by Adam: while he no doubt enjoyed this respite where he could be a normal father, John couldn’t escape the fact that he was a Hunter with a two-decade long mission that he wasn’t just going to walk away from. At the same time, this mission had nothing to do with this newly discovered son disrupting his normal life to have him help avenge the wife who’d died about a decade before Adam was born would have been cruel. In the end the best way he could see to protect this kid from all of that was to keep him in the dark entirely. He also kept Adam’s existence from his other sons because he’d already chosen not to include the boy in their Hunting lifestyle - it wouldn’t have been fair to tell them they had a brother that they could never have any contact with.
At the same time, John’s decision came from a darker emotional place. Seeing as he wore his wedding ring until the day he died, he probably felt guilty as hell about “betraying” Mary: it’s one thing to have sex with other people, as he could always say it was just to satisfy a physical need, but having a child with someone creates a more emotional bond - one that he’d only shared with his beloved wife. He might have also worried that Adam’s existence would justify Sam’s perceived abandonment of the mission and diminish it in Dean’s eyes - after all, if John was moving on by having a child with another woman, why shouldn’t they also move on? Finally, there wasn’t a good way to explain to his sons why Adam got to have the normal life that Dean had been denied since he was four and that got Sam kicked out of his family for wanting to pursue. Does this make John a bad person? Of course not; it just makes him human.
In the end, John was both right and wrong to keep Adam (and presumably his mother, Kate) in the dark about his real life while keeping the existence of another brother from Sam and Dean. Adam got to grow up, go to college, and have the normal life that had been denied to his older brothers while Sam and Dean developed a bond so strong that, tattered as it currently is, is capable of surviving the Apocalypse. However, Adam’s lack of knowledge of all things supernatural and the boys’ lack of knowledge about Adam ended up killing or endangering each one of John Winchester’s sons: Adam was completely vulnerable to the vengeful and bloodthirsty ghouls who wanted him dead just for having the same DNA as the man who killed their father, and those same ghouls were able to use the kid’s existence as a weapon against the remainder of John’s progeny.
The struggle between pure and selfish emotions, deciding what the right thing is, and having it be not enough is revived when Dean and Sam found out about their half brother. The selfless part of their emotional responses was all about doing what was best for the kid. For Dean this meant protecting him by keeping him away from both the immediate danger and the Hunting lifestyle. The reasons behind the immediate danger were obvious - something terrible was coming after someone with no Hunting skills or experience with the supernatural - but there was a lot more to him wanting to keep Adam from becoming a Hunter. There was the obedience to John, who he guessed kept the kid out of it for a reason; there was him learning the lesson of watching Sam lose his innocence over the past few years and not wanting to revisit that on another innocent; and there was Dean’s underlying self-esteem issues in his belief that Hunting isn’t a good enough lifestyle for Adam or anyone else who has a choice. He said it in Wendigo: he accepts that he and his family are screwed but he carries on through the horrors and indignities to save other people from becoming like them. While finding out about another brother threw him for a loop, Adam was still a civilian and someone he could save from this fate.
Dean was also motivated by much pettier emotions, namely resentment and jealousy. That he was jealous of John’s supposed relationship with Adam, not only because their dad took the kid fishing and to a baseball game but also because Adam got the father that Dean had before the fire without having to deal with the father that was there after the tragedy, was no surprise, but he also resented Adam’s intrusion into his life even without the daddy issues. Hunting was his life, his connection to his father and brother - those emotional scars may not have been pretty, but he’d earned them. Why should Adam get both the white-picket-fence childhood and a place in the family business without going through the trials and horrors he and Sam did? Seeing Sam and Adam bond must have fueled his jealousy and insecurities: he had to have asked himself how it was that Sam could get along so well with a brother he barely knew when he was so out-of-sync with the brother who raised him and literally went to Hell for him. Dean once said that John and Sam were all he had - it’s only natural that he felt threatened by the presence of a new son, a new brother.
For Sam, doing what was best for Adam meant understanding, supporting, and preparing him. Sam related to Adam, from his shock of suddenly having to carry on after losing all that was left of his already fractured family to the frustrated question of “Do I get a say in this?” He’d had a lifetime of having little-to-no control over his life thanks to the protection of others; he could understand the need to try to take control of an unthinkable situation and support this choice by showing Adam the ropes. Sam also understood the dangers Hunting would have on the life Adam was leading in a way Dean couldn’t because he’d lived it once himself: Jessica was murdered for no other reason than Sam was in her life. While it seemed harsh to tell Adam that he would have to cut everyone and everything out of his life if he was going to pursue Hunting, Sam knew Adam needed to be prepared because walking away now was a whole lot easier than realizing too late that he couldn’t protect everyone he cared about from everything. Some things are too important to be sugarcoated.
At the same time, Sam was also experiencing resentment and jealousy. All he wanted as a teenager was to be normal - something that Adam had managed to achieve, thanks in part to their father. Sam couldn’t help but feel jealous after finding out that John did what he could to ensure Adam had a normal life so soon after banishing Sam for daring to try to have the same thing. Dean’s determination to preserve the kid’s normal life must have also stung because his brother actually wanted Adam to have a normal life. With Sam, Dean only wants him to want to have a normal life, the same way that as a little girl I wanted to be grow up to be She-Ra, Princess of Power (He-Man’s twin sister, for those of you not familiar with the 1980’s cartoon) - a cute, impossible dream to hold onto only to maintain his innocence but otherwise let go of as he grew up. The desire to be normal was the source of conflict between Sam and his family for many years and to have that life for Adam be respected and protected both John and Dean no doubt left a bitter taste in his mouth. Adam was a Winchester, after all, and to Sam being a Winchester meant that any sort of idyllic, normal existence is automatically forfeit.
In the end, the fact that Adam was dead before they got to town meant that the boys were both right and wrong. Dean was right in that Adam wasn’t ready to face whatever was after him but wrong to think that keeping him from Hunting was enough to keep him safe. Sam was right in his belief that being John’s son as well as a Winchester meant he couldn’t be protected from evil just by not becoming a Hunter but wrong to think a day or two of training would make any difference in that fight (after all, Sam had a lifetime of experience and still barely made it out with his life). Like father, like sons: with their personal life experiences and very human conflicting emotions, they made the best decisions they could but ultimately couldn’t keep the supernatural world from closing in on their half brother.
As tragic as what happened to Adam was, this experience gave the boys a better understanding of their father and each other. Hearing John’s words come out of Sam’s mouth and recognizing his father in his brother’s responses jarred something in Dean, making him see beyond the hero worship perceptions to see the man his father was. Sam was able to get past much of his stored-up anger at John by realizing his father’s blunt and often harsh life lessons were John’s way of trying to protect him. It’s always surprising for a child to learn that for better or worse their parents are only human.
That’s why Dean’s comment to Sam about how much he was like John wasn’t a compliment, an insult, or even a warning: it was just a fact. John’s all-to-human strengths and failings are something both boys need to acknowledge and understand if they’re to keep from repeating their father’s mistakes.
That alone is reason enough to be glad Eric Kripke risked jumping the shark by giving Sam and Dean a previously unknown long-lost half brother.