Rubbish. Chesterton said that if people don't believe in God they believe in anything. He was not talking about me or himself. He was talking about everyone. Now either he was right or he was wrong, but he was making general claims.
Well, I agree with you. And here is the crunch. Does it make a positive impact on society to have witchcraft revered as some sort of realistic, respectable doctrine? To have Wiccans honestly (in their mind) describe their cult as some sort of morally based ideal? I think it is in society's interest that such people be countered. Surely you agree that Christianity must be supreme above pagan, immoral superstition?
Since it is a general claim, it is refuted by a single counterexample. Once one finds a single individual who does not believe in God and also does not believe any old notion that is presented to him, Chesterton's claim falls. It is quite easy to find such individuals (the late Isaac Asimov is the first example that comes to mind). QED.