I used to have an issue with it, but after years of it bugging me, and having in and outs with God, and gaining my own personal revelation on christianity and belief, I came to recognize that, at least with the simpsons, it's not so much the belief they're mocking, or even God. What it is they're poking fun at are those Christians that live that holier than thou lifestyle, which there a many of, and quite honestly, a lot of them paint christianity as a whole in a bad light, because they put themselves on a pedestal, and make others around them feel so much less, which is far sadder than any cartoon poking fun at that type of personality.
There are definitely cartoons that do mock God, which I do think is wrong. But there's a difference between mocking God or belief in God, and mocking the religion. A relationship with God goes far deeper than any religion designed by man, which for some people christianity is. Don't take it to personally. Know what you know and share that.