If someone starts deluging you with unwelcome Personal Messages, that's another matter, and you'd be right to complain and ask that they be blocked. But when it comes to posts on threads, it's best to do the filtering direct by just sliding past them without reading them.

That's where unnamed GUESTs screw things up a bit, because they all look the same, so you can't pick and choose. Best thing is to slide past them all anyway.