They were so very violent - almost for the sake of violence. The RoadRunner cartoons weren't like that. But in either case, in cartoons the characters get up and play another day. AFAIK, they don't in these games. In most games I've seen, there are no significant consequences for smashing up your car or blasting the wrong person.
It's not a 1:1 causal thing, but children and young adults are influenced by the things they see and experience. Kids have to be taught how to become bullies and criminals, it seems to me.
I don't know anything about GTA-SA, so I can't really comment on it. But I personally take the ratings under serious consideration when getting games for friend's kids.
There are always exceptions, of course. Luck!