Note: A lot of my friends have written extensive metas on their characters, and I actually have a lot to say on my personal head canon for Dean and his psychology. However, instead of posting it in one giant chunk, I'm going to write a series of individual essays, and create an index pinned in his journal to all of them. This is the first of those.
Each of these essays are not me saying I know everything about Dean and this is the only way I will ever look at things: rather, I invite people to discuss, question, or argue with me in the comments to each one. There are still episodes of the show I've only seen once or twice, and so I'm bound to have forgotten some things; if you know details of the show that contradict my ideas, I'd appreciate hearing them so that I can amend my personal view of Dean, and play him better. :) Or if you'd simply like to discuss the kinds of things I'll be talking more, I always love talking about Dean.
Daddy Issues & the Batman Complex
Dean’s relationship to John, hero-worshiping issues, and the impact of secret identities.
Dean and Sam's differing views on hunting have a lot to do with their respective childhood experiences. Dean remembers what it was like to have a normal life, family, and home, and he's had to watch how losing all that transformed his father. Given that the loss of his mother was something very real to him, unlike it was to Sam, it's hardly surprising that Dean chose the subconscious route of justifying his father's transformation, rather than condemning it, because this allowed him to not also lose his father, so to speak. If he accepted that the path his father was taking was not a healthy one, or chose to be resentful about it, it would put a wall between them that would leave him without any parental figure to look up to, and the loss of his mother hurt him too much to be able to willingly accept that and make that choice. Instead, it was easier, and more conducive to his relative sanity, to simply find reasons to believe that all his father's actions were just.
So how did a very young Dean grow up justifying the questionable actions of a man who ripped his childhood from him, and his chance at a normal, real life or identity? How did he come to practically worship a father who was bent on vengeance, and showed more passion for his obsession than love for his children?
Very easily, actually. He simply applied a child's lens to things.
He believed that his father was a superhero.
It's a common enough childhood fantasy to think that one's mom or dad is a secret crime fighter, but in Dean's case, he had every single reason to believe it. John Winchester used aliases everywhere he went, making who he really was into the secret identity he only shared with spare friends and his family. He didn't have to hide behind a mask - this was modern America, and we're identified by our paperwork. Fake IDs, passports, credit cards - they were all as good as a mask, or better. Sharing in his father's secret became empowering for Dean, and was one reason he's always been so determined not to share it willingly. Next to ordinary, every day people, John's occult knowledge and martial skill would seem practically like superpowers to a child. Though that perspective, having his father pass that knowledge and those techniques down to him was a particularly sacred type of apprenticeship. He was expected to carry on his father's legacy, fighting the forces of darkness, while sacrificing his own normal life for the greater good. It was every child's dream: it was Dean Winchester's reality. It's no surprise also, then, that he took to the role with so much enthusiasm, and attempted in every way possible to imitate his father.
Dean's mimicry of his father extended to more than just learning the tricks and trades of fighting the supernatural. He also mimicked his father's "costume" - wearing the same sort of battered leather jacket and same style of clothes as his dad. Sam points out that Dean even listens to the same music as their dad, and Dean is deadset on not even trying to listen to anything more modern. Being given the Impala by his father was a huge symbol to Dean of "becoming" his father, as he long hoped to do, as the Impala was as symbolic of John's heroism to him as the Batmobile was to Batman.
Speaking of whom, it also only makes sense that Dean's favored superhero is who it is: if John Winchester is any sort of superhero archetype, it's most definitely Batman.
John and Dean might not have come from a family of wealth and privilege, but they find a lot of their wealth in freedom - and with a string of fake credit cards, money's never been something Dean's really had to be too anxious about. But the real Batman similarities lie strongly in John's motivations. Bruce Wayne transforms into Batman so that he might enact vengeance on the one who killed his family - and anyone like them. He felt his action were tied to the greater ideal of justice, but in truth, they were rooted in a very personal desire for revenge, that turned his personal crusade into an obsession that warped his entire sense of reality.
Unlike Superman, or other heroes whose powers are derived from some supernatural source in and of itself, Bruce Wayne's powers came simply from his own resources, physically, mentally, and tangibly. To Dean, this seems the ultimate sort of hero: someone normal, who through their own cunning and training turns themselves into something that the dark side of the world needs to be afraid of.
Most importantly, perhaps, Dean's view of his father as a superhero did a huge number on the development of his actual personality. When it comes to hunting, Dean's serious, sharp, and dangerous, but when it comes to interacting with people outside of this context, he's come to view himself as presenting a "secret identity" of his own. Problematically, when this is the majority of the interactions he has, this becomes his prominent personality, so that he, for all intents and purposes, is the face he chooses to show the world. Just like with Bruce Wayne, most of this personality is designed specifically to keep others at bay, to throw off suspicion, or to disarm others so that he might extract whatever he wants from them. Bruce himself comes off as someone entirely self-involved, irresponsible, superficial, and hardly heroic by any definition of the word. Dean comes off as equally self-involved when he is in fact, probably the most selfless character on the show. It's that selflessness, actually, that keeps him from wanting to advertise the fact, so that he won't be celebrated for the trait. In the same way, Dean's incredibly responsible when it comes to things he actually cares about, and he prides himself on the fact, but you'd be hard pressed to find someone who would actually call Dean responsible. Dean's personality seems incredibly superficial, given his tendency to turn even the most dire situations into jokes, but he knows exactly what the reality of the situations he's dealing with are, and he doesn't screw around when it comes to the safety of others.
Dean's 'secret identity' personality is also what is responsible for his inability to connect with others readily. It's his natural instinct to hide things about himself from people, whether they're the reality of what he does, or simply the truth about what he's feeling in any given situation. Having any of this laid out makes him vulnerable, and puts his entire "quest" at risk. Obviously, it's much easier for him to keep relationships with others on a superficial level, and this is especially applicable when it comes to women. He maintains the same sort of tendency towards a number of casual surface level flings that Bruce Wayne has, more to cultivate an image of himself (and as part of the coping mechanisms I'll discuss in a later essay) than anything.
Even Dean's perspective on Sam is influenced by this superhero lens. In almost every superhero story, the hero keeps his identity a secret from those loved ones in his life that he needs to protect, and who wouldn't be able to handle protecting themselves. The fact that Dean knew their father's secret for a long time before Sam ever did, meant that during those interim years, that's how he saw Sam: as someone who needed to be protected, which is obviously a sentiment that has stuck with him for the entirety of their lives. Sam's inability to look over their father's flaws, which Dean has always justified as simply necessary evils, is a threat to Dean's carefully constructed fantasy about their lives, and is why it's such a point of emotional contention between them. Very little is as effective at getting Dean pissed off quicker than when Sam attacks his view of his father.
Of course, as the series progresses, Dean is forced to face up to the possibility that Sam is right. Dean's been able to make it to his late twenties without ever having to really grow out of his childhood fantasies, and so it's especially difficult for him to try to realign his way of looking at the world at this point. He still continues to scrabble to justify his father's actions, but the truth is, that the attention his father always directed towards Sam, as a result of Azazel's plans for him, made Dean feel as if he was always second best, no matter how hard he tried. There's a level of resentment that simmered under the surface of Dean's relationship to John, that despite toeing the line to an extreme degree throughout his life, he still got cut less breaks than Sam ever was. Given the degree to which he hero worshiped his father, and aspired to be like him, so much of his self-worth became tied to his father's approval, and the fact that John rarely ever evinced it is one of the main reasons that Dean's seeming egotism is nothing more than a front for his incredibly low sense of self-esteem. The fact that his father managed to last as long as he did under Alastair's knife without giving in, while he gave in after only thirty years was just the nail in the coffin of his self-delusion that he could ever be the kind of hero he sees his father as.
By current canon, Dean's been forced to face some of his father's more questionable decisions at face value, and been sent back in time to learn that his father used to be a perfectly normal person, both of which rearrange Dean's own ideal end game. Dean used to think that there was no reason he would ever want to hang up the cape, so to speak, but now he realizes that what drove his father was the impossible desire to be able to return to that state of normalcy. Dean ends up reversing roles with Sam: he wants the white picket fence and family, and retirement. Problematically, however, at the end of the 5th season, his experiences, his time in Hell, losing Sam, and his anger at God all culminate to one very terrible truth: there is no going back for him, because he will never truly escape what he's been through, like a veteran returned from the worst of wars. Just like his father, just like Bruce Wayne, just like so many heroes, his identity is the hero within, and escaping it may simply be an impossibility.