They are good because they are purely for enjoyment and the children know that. If some kid is hitting his own head with a frieing pan its not the shows fault the kid was probably an idiot in the first place. Also they help with reliving stress not just for children. I mean have you seen how happy bronies and pegasisters are?
Cartoons are good for your brain because it releases creative activity to the young brain. Yes it is bad to watch too much cartoons, but with the right amount per day it is actually healthy for you. Cartoons can create ideas in our next generation's minds. Also if a child is lonely these cartoons help them, like a friend.
I am fourteen and as i was a kid I stopped watching tv and as i got into the cartoons i realized that that idea was already taken so i stopped using those types of games yes there are some good cartoons for kids that inspire creativity but those shows are short and far apart.