I think I'd "behead" subthreads at posts by blocked users, so their posts and any replies under them get hidden for me. I'm happy enough to lose followup discussion and/or arguments against anything a user who I've caught out not reading the actual post and replying - and been annoyed enough at too add them to my blocklist. I _might_ miss some interesting discussion that way, but I'm fine with that to be the cost of me avoiding getting irritated by annoying posters.

(And the mood I'm in right now, I'd probably block top level posts by blocked users as well)