NotUmbongoUnchained, you can't dictate the way people respond to your thread. It's clear from your repeated posts that you wanted people to give a simple yes or no, and that you'd ignore the nos, but kids being exposed to inappropriate material is a huge issue of modern parenting and it's pretty obvious that people want to discuss it.
I think it's especially important to recognise how things have changed. If you were that primary school kid in the 80s/90s who saw Freddy Krueger or whatever, you got a solid amount of bragging rights and the prestige of scaring the crap out of any other kid who'd listen. But that was it. There wasn't much worse you could realistically get.
Now, we're all a few clicks away from the most dismal, appalling range of graphic violence, gore and porn imaginable. It's increasingly difficult to truly monitor and limit kids' internet access; of course, at three it's not a problem, but throughout primary school it gets harder to guarantee they're not seeing anything awful (on a loosely-supervised visit to a friends' house; on an older kid's phone) and once they're at secondary then that's pretty much it.
I don't know if people think exposing their kids to studio-produced superhero-featuring torture and violence somehow builds resilience to this; that kids who've see a good measure of moderate nastiness already won't be curious about the truly bad stuff. But I don't think that works. Most studies show that the tolerance or appetite for this kind of thing only increases, and that many young people who've become totally blase about mildly unpleasant stuff eventually move on to more extreme imagery. There seems to be this element of the human psyche which really enjoys the jolt you get from fictional representations of sex, violence, murder etc, and if you overdo your exposure then the type of image needed to give you that jolt becomes more and more extreme.
Obviously, this is a wider pattern; plenty of people watch slasher movies without moving on to snuff porn, and nobody's saying this one kid watching a 12-rated violent film is going to develop psychological problems. But, overall, it's an issue that didn't really exist in the 80s or 90s, and what we need to question now is: assuming our kids will, one day, have the ability to access material a trillion times worse than anything pre-internet generations could realistically have seen, how careful do we need to be in their earlier years, when parents do have ultimate control over what their kids see?
You clearly have some awareness that certain films aren't considered suitable for younger children, or you wouldn't have asked. Do what you feel's best for your own kids, but don't bitch at everyone for participating in a debate you started.