Are we talking about actual injuries, or just depictions? There are lots of ways to depict things without taking a photo of it actually happening. People don't usually have the empathy reaction to something the know isn't real.

Just consider all the action movies where people get shot all over the screen. People seem to love that sort of movie, yet most of them would probably pass out if they saw someone shot in in real life. For some reason when it's fake, it's fun, but when it's real, it's horrifying.

So the fake/real distinction is pretty important. Even when we're talking about people fantasizing about it happening to themselves, that's just another kind of fake. Probably not many people who enjoy that fantasy would also go for it in reality.