One thing about self-moderating threads is that the OP can remove any post that doesn't comply with the rules, is spam, or something like that. So even if you both respond to some users who don't read the thread rules then eventually the OP will delete the post after realizing it.

So I don't think it's always good to respond to some rule breakers or who don't read the rules even if your intentions are good. It can also bring down multiple repeat posts in the thread.