Nobody's mentioned the episode where Ned's wife is killed, and I really thought that was a watershed moment in the development of the character. That episode was a while ago (and so I don't remember it very well), but I was really surprised at how positive a force Christianity was portrayed in the lives of Ned and his family. Most of the time, yes, the Flanders are simply stand-ins for Christian simple-mindedness. But every once and a while we're reminded that they
are serious about their religion, and that it
is, on balance, a positive force in their lives.
Christians need to realize that the Flanders represent Christianity as it is practiced by Christians. Often, that's a positive force. Sometimes that's a repressive force. But that's the spectrum of Christianity, and if Christians aren't happy with that, then they need to clean house.
P.S. That episode was "Alone Again, Natura-Diddily" and it aired Feb 13, 2000.