I'm a well read grad student who's bluntly honest about all things, although I try to be most honest about myself.
It's just brutal, violent, and all about holding drug dealers responsible for the harm they cause. It's some really nasty, horrible people - don't even get me into what The Face does because you do not want to know - getting killed by a one man army with a burning need for to see punishment dealt out to those who've been truly naughty.
It's a wish fulfillment fantasy. It's a catharsis that can see such wrongs righted, without crossing the line Castle has. Yes, I love him, yes he's a favorite character, but part of me is also repulsed by the lengths he goes and the manner in which he deals out said punishment.
Also, Castle drops off the kid he's been protecting, the one whose father was using her as a bomb against Castle - well, he tried to anyway. He buys her an ice cream and leaves her there, and when the authorities find her, one of them, nearly at the breaking point, just starts cursing.
Then this happens with the police officer:
I don't know why that made me laugh so much, but it did.