That's interesting... I think it alters us in one way or another. If I watch a romance unfold for 90 minutes I walk away with renewed clarity of that gap in my own life. But that involves emotional need, where your example addresses emotional catharsis. I think one similar example that fits your account is basic comedy... we go to a movie and we experience the comedy of life and that's enough; we rely on the fiction for the comedy; we don't need to seek to create it in our personal lives. An emotional experience like revenge or justice seems to be somewhere in the middle; while it gives us a certain release, it also awakens a certain need. I'll think about this the next time I walk out of a vigilante-oriented movie.

i've felt what i would describe as a cathartic reaction to some films. i watched rent during a time in which i'd been neglecting my interests in favor of someone else's, basically everything that i was passionate about as far as artistic expression. it reminded me of the world i'd sacrificed and wanted to experience, but wasn't. by watching it i felt like i was in that world again for a little while. (the lyrics were extremely moving, the characters were strong willed...) it caused me to be inspired rather than apathetic.

to me, a movie's a movie. vengeance films pull at my emotions, though, because on the one hand i want justice to be served to those bad guys. so when Connor and Murphy MacManus kill all those bastards in The Boondock Saints, it eases the tick in my brain that wants the bad guys to choke on their Cheez-Its.

but, in real life, i don't think it fair to take anyone else's life, regardless of their history of evil acts. it's just not right, in my opinion.

so, for me, the vigilante films just feed my human tendency to want assholes to die.