I don't see thier brilliant responses to my discourses now but as you say lurkers do or whatever. That is polluting my discourse and I did not want to talk with this person anymore.
Nope. The discourse ended when you abandoned it. Whether the other person is still shitposting is something you have no control over. I guarantee that if they were enough of an asshole for you to want to block them, any lurker worth their salt's already aware of their assholishness. And really, it's kind of silly to concern yourself with the opinions of people who might or might not even be there.
Stop thinking of these exchanges as debates you need to win, and think of them instead as conversations that either are or aren't worth your time. When you block, you're making a decision the conversation's not worth any more of your time, so stop giving it your attention--and that includes wondering what else has been said and what others think of it.