I don’t think public institutions should be able to make that call. Private institutions and individuals, sure.
Why not? Public institutions are supposed to serve the public’s interests.
Because I don’t want to give some unelected bureaucrats the ability to discommunicate someone because they said something stupid. Public goods are meant to serve the public, even if they have bad opinions.
I think the limit should be pretty high, but I’m fine with, as an example, people who spread abject hatred being rejected by most parts of society. I think not spreading hatred against your fellows is an integral part of the social contract.