I think you may have been giving them too much credit. Here's an adherent explaining that wireheading is a bad thing, but in heaven, wireheading is good because everything in heaven is good.

I don't think people don't always put much effort into critically considering their beliefs.

I had an idea for a sort of Christian fanfiction, in which people marked for heaven and people marked for hell both go into the same firey pit, but the former are wireheaded to be happy about it. It's a far more efficient construction that way. (I suppose you could also do the reverse, with the people marked for hell being reverse-wireheaded to find nice things agonizing, but that doesn't have the same tasty irony.)