Muting is a good first step but it doesn’t really prevent harassment. People can still comment and everyone who follows you sees those comments unless they mute that person too, which is doable but not a great default experience. Maybe web of trust solves some of this.
Discussion
I guess a nip could be created to attach a block-list of npubs to one’s own account. Nostr clients would have to adopt the standard and not display the block-list of the original note author. This would give everyone the choice if they want to display blocked comments or not. As a user I personally don’t want to see spam replies in most cases and am grateful if a note author is maintaining a spam-filter for their replies. If I’m curious anyway to see a particular blocked reply anyway, I could always opt-in to see it.