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.
Just like me doing a countdown without reading the rules on v1 which the OP has now locked.
Not responding when someone makes a countdown to the next rank can be a response to that person that something went wrong.
But by responding and admonishing that the person has violated the thread rules, it's also not wrong, even though the OP can delete when deemed not to comply with the rules.