Cartoons and children shows are a lot easier to understand they require less thought to understand them. Many adults look for something a bit more mentally or psychologically challenging. Add to that...
(Personal Opinion) Because they cannot imagine there life as a cartoon. In 2011, there are more "reality tv" shows than there are anything else... Why do you think that is? (And how much of reality...
Because you're getting your information on what's "acceptable" from the wrong people. If an adult wants to watch cartoons, there's nothing actually wrong with that; it depends on what they like to...