Exposing oneself to disturbing things

[If anyone's here from Iron Blogger, welcome!]

Home for the holidays, I've been rewatching a few Firefly episodes with my family. Because everyone gets to pick, said rewatching has not consisted solely of "Heart of Gold" over and over and over :) -- and I end up watching the episodes with disturbing bits that I don't like.

What don't I like? I don't like stabbings or incisions (and I'm not fond of injections either, or at least the needle-entry part, though IVs are OK). I don't like torture scenes. I don't like when characters walk alone through dark creepy hallways where it's implied that Reavers or similar will suddenly jump out at people. I don't like half-rotted or mummified corpses.

I'm not sure what the common thread is between these things -- or between the things I don't mind (blunt trauma, gunshots... or most anything not listed above).

Somehow I keep making myself sit through movies that have this stuff. I managed to freak myself out pretty badly at a free showing of 28 Weeks Later a couple of years ago, when I could have just got up and left. Perhaps I feel it's unseemly for a grown, voting adult to have to not watch things. After all, when I was a kid I didn't have any compunction about leaving the room when it got to the Emperor-electrocutes-Luke scene in Star Wars. My dad's philosophy on scary things is that he leaves the room because "I don't need that stuff in my head, it's not worth it", which strikes me as very sane. What, after all, is the higher purpose served by my watching Mal and Wash get electrocuted repeatedly?

However, I feel that there should be a corresponding policy to not avoid watching (or reading about) the horrific things that go on in the real world, because in that case a horrified reaction can translate into a call to action (charitable giving, political action, whatever). This is actually one of the strongest arguments I've heard in favor of free speech, and in particular freedom of hate speech: let's get it all out there so everyone's at least aware that this sort of badness exists, rather than letting it stew in private gatherings until it becomes hate crimes.