I staked out a "Yeah, whatever ..." position on Harry Potter 4-5 years ago, and I'm still there :-). My oldest boy just read the first one this week, and said he liked it well enough to check out the second.
Literature is full of characters who aren't exemplars of Christian perfection. Dear General Patton, for example ...
Read it with them. My mother got in to it a few years back and now she helps us read aloud when we get the book. Plus you'll feel better about it. It's something we all like - 22 down to 10. Nice family time.
How old's the boy? The books get darker... I wouldn't really recommend them for anyone under nine or ten.