If someone makes a threat on a person or groups life online, or doing something illegal, then I agree it shouldn’t be allowed. But censorship today goes far beyond that.
The purpose of the platform matters. MSN chats (group chats?) and sub-reddits are smaller places presumably set up by another user for a specific purpose. I have no problem with people being banned/censored for whatever reason from these smaller forums.
I have an issue with censorship when the platform is generic, not dedicated to a particular topic or group, like Twitter, YouTube, or Reddit as a whole. When one or more dominant third party platforms censor the same people, it has an effect similar to that of government censorship.
I also think the censorship will backfire, because by being shut down, it gives power to the ideas being censored. “There must be a reason they are shutting down discussion. They have no real answer to it!”
I agree that online harassment is ugly, but I still believe in absolute free speech on these generic platforms. The best solution to all of this would be to have block lists that people could opt-in or out of. Don’t want to see something? Subscribe to the block list.