I'd be great if the block would make them unable to downvote you and your posts as well. And it'd be nice if it wouldn't even let them reply to your posts.

I'm not entirely sure that's going to work out the way people think it will.

Suppose I'm some jackass that gets off on harassing you: if blocks prevented me from interacting with your content, and you blocked me, I would have confirmation that I've successfully gotten under your skin. I can then just make another account and continue what I'm doing.

If blocks don't notify or provide indication to the blocked party, they would either escalate their behavior (while you are blissfully unaware) and get banned by a moderator, or give up and move on to someone else.

There's also considering how that's going to work with moderators and admins: do they get to bypass the block and continue to comment and interact with you against your wishes? Does it hide your posts from them if they're blocked? It's a lot harder to design this type of blocking on a community-centric platform than it is to do for a microblogging platform like Twitter or Tumblr.

Because muting doesn't stop the poison the spread, just my personal ability to not see it.

That's what mods and admins are supposed to do. It's not the users' responsibility to moderate the behavior of others, and it's a lot less stressful than trying to stop toxicity when you only have words in your moderator toolbox.