That is the same reaction GAF has to everything about porn and videogames.
Remember that a lot of posters are young and/or stupid (and sometimes with Gata you get the perfect combo of both).
I think the thing that is most revealing is the defense that 'well my parents were really shitty and let me play GTA when I was 6 years old so it must be ok for everyone!'. No, you had shitty parents that did not care about you and would rather you shut up instead of have to look at you. You probably also have a lot of other defects that are not apparent to you or us on an internet message board.
I do remember watching violent movies when I was a kid, but that was like 10 and up. My parents, and most of my friends parents, did not have a problem with violence at that age but nudity was a big no no. Which is weird but I think I will be the same way (though I will probably make them wait a little longer to see some violent shit and I will never want to be in the same room as my kids if a sex scene comes on).