I disagree. On a public forum no one should be able to control what content i see and what content i don't see. If you're going around saying bullshit in a public forum, i should be able to see that, and i should be able to post a public reply refuting your bullshit. Otherwise people could post bullshit and block everyone from replying who would show that their post is bullshit. You shouldn't get to block people from rebutting your claims.
EDIT:
Though i could see the usefulness of an automatic tag on their comment saying "the OP has blocked this user, so OP doesn't see this post."