Society functions fine without these platforms. Their bans will work out ok.

Well, they didn’t ban him because he thinks wrong things. They very clearly banned him because his words on the platform were intended to cause violence and stop the democratic process in the US (but mostly only the former). I think it’d be foolish not to ban people who use Twitter to communicate plans to perform acts of violence. If anything I hope they (along with other platforms) use this opportunity to get better at it.

Don’t forget this is Twitter exercising its right to free speech. If Trump is upset, he’s free to do the same and make his own Twitter-like platform. I’ve seen a few open source ones posted here that he could fork.