I had a rousing debate with a woman once about this. She wouldn't even let her children watch things like the Power Rangers etc... It was too violent. Me? Mine are 12 and 9. They can watch pretty much any horror film that they're interested in watching. (Although the 9 year old's more of a wimp for them so we let her choose the 'scare level'.)
Her whole point was that children cannot tell the difference between fantasy and reality.
My whole point was that children deserve more credit. (That, and as a parent you should be discussing these things with them!) A child could watch Sylvester get clobbered over the head with a shovel, and laugh. The same child could then go for a walk with their parent and watch a pedestrian get smoked by a car at an intersection. The child would be horrified, hands down.