As others have said, this movie wasn’t nearly as bloody or violent as the first two. I took my brother to see Interview With a Vampire - which was rated R instead of PG-13 like this movie - when he was 11, and he hasn’t grown up to be a psycho, vamp loving killer, so maybe little kids can handle a few vampire movies and not grow up “badly raised.”
Once again, the research does not say that kids exposed to violent images all grow up to be psychos. Claiming that as the yardstick against which to judge the impact of violence is an obvious strawman that you throw up so that you can tear it back fown to “prove your point”.
Exposure to violence acts to increase aggression. That is different than turning into a psycho, and in come cases it is useful (ask the Marines.)
I say if you are going to take a young kid to an R movie, make sure it is R rated for lots and lots of nudity instead of violence. When my girls are grown up, I sincerely hope that they will be exposed to naked bodies and even “GASP!” sexual situations. On the other hand, I hope that they will never be exposed to a running gunfight and bodies being chopped in half.
Nitpick: While I agree with your point, Blade: Trinity is rated R, not PG-13.
This, of course, after the inevitable McDonalds-Burger King merger.