If it's painful to you, you're doing it wrong. At 8 you should get him to the library and let him chose himself what books he wants to read. Also, you don't have to like the books he choses. You despising his book choice is irrelevant.
If I just let him do what he wants he just plays on iPads or computers in the library (iPads have bunch of games installed, computers do not have games but you can obviously play Web-based stuff etc). He doesn't care much about books unfortunately. It's my job as a parent to make sure he does read something (I'm trying to find something he likes and something that's more of a long form as opposed to a comic). I do realize that the more I pressure him the less he likes it but I'm doing my best to find balance.
As for choice of books, both Dan Pilkey and Dan Gutman are considered controversial authors and a lot of parents feel uneasy about their kids reading their books. Check parents' reviews on goodreads or any other site, you'll find plenty of negative reviews, it's not just me.
I won't stand for Pilkey slander. I have worked in education. His books are certainly silly, but they are indeed a very functional gateway to get kids to enjoy reading on their own. Yes, they are immature, they are for kids. No, they won't make your kids into delinquents, especially not if they get your kids to read a lot more than they would have. I think it's important to show kids that reading doesn't have to be all textbooks and dry academics, it can be fun and enjoyable, because why would they ever read of their own volition if by their perception it isn't fun at all?
From reading reviews of Dav Pilkey's books in Goodreads I didn't see anything like you describe, is it getting banned by the same fundamentalist Christian parents attacking public libraries in the USA or something?
Reviews are pretty good, most books hover on 4+ ratings.
