Personally I don't think I'd waste the energy getting worked up over it. There's nothing that you can do about it, so is there a point in getting frothy over it? Is the guy a dick? Yeah, pretty much. Would I buy his books? Not in a million years. So there's $8 is publisher isn't getting from me, and that's about the extent of "showing my displeasure" that I can do in the real world.
Take into account, however, that over the past 18 months, my life has taken a serious left turn when it comes to "things that I think are worth getting upset about", and things that I feel are worth expending my limited energy over are much fewer and farther between than they used to be.
If you feel strongly about it, write to the publisher. I doubt that they'll care, but since they're the ones who are impacted by the books not selling, they'd probably be a little more financially interested. I doubt the author cares - there's no way he's stupid enough to not know that Wicca is a religion, and he chose to use it anyway.