HBP SPOILER!!!!!!!!! don't read unless you want to. you have been warned!
this entry is based off of the summation posted here. scroll down and read the part about snape.
it's possible that snape only killed dumbledore because dumbledore was ordering him too. i don't see dumbledore as the begging type--he was pleading, but i am starting to agree that he might have been pleading with snape to kill him. it would appear to everyone else that dumbledore was looking weak, but snape would know the truth. this appearance of weakness would have made snape mad--snape looked mad . . . is it possible that he looked mad because he realized that dumbledore had put him in the situation to force snape to kill him? shoot, if i were snape then i would be pissed off too!--now it looks like snape is the ultimate betrayer. if that's the case: he's kind of like siruis was, isn't he? he will have to stay in hiding, and try to keep the good guys from killing one of their own--particularly if they win this war!
i can see dumbledore and snape arguing about this too . . . they did argue about something, and it was probably because dumbledore was telling him--"if you can't get to me before the death eaters do--assuming that's the case--you're gonna have to kill me" and snape would have been like "oh HELL no! this is getting too hard. i don't wanna double agent if it means that i have to look like the bad guy when all along i've been the GOOD guy!"
on the other hand . . . you do have to really mean the killing curse. the never-ending optimist in me wants to believe that dumbledore was right. but still--it seems like a really stupid plan at this point.
~L