You can 100% mute and block people on Twitter, Facebook, Instagram, most main line social media platforms. Hell you can even mute keywords on Twitter and never have to deal with seeing another tweet about Will Smith slapping someone.
Should one user be able to decide if another user should be expelled from a platform? That leads to a lot of sticky problems, so no, they shouldn't have that power. Should a user be banned if they violate the terms of the platform (roughly what mods on IRC would do when a user was banned)?
Yes. Yes they should. And they do. It's a liability for platforms to not enforce their own rules.
The issue is that with twitter, you can only ban a user from interacting with you, or from interacting with the entire platform.
Traditionally, there used to be something in between: Ban someone from your small sub-community.
And moderators on most social media platforms only take action if they have to, preferring to stay inactive, while in most social circles people would proactively make sure a new member is a good fit.
Should one user be able to decide if another user should be expelled from a platform? That leads to a lot of sticky problems, so no, they shouldn't have that power. Should a user be banned if they violate the terms of the platform (roughly what mods on IRC would do when a user was banned)?
Yes. Yes they should. And they do. It's a liability for platforms to not enforce their own rules.