If this were your platform and its T&C explicitely said that harmful content is not allowed, in my opinion it’d perfectly fine that you delete a comment you deem harmful.

> "I disagree with what you say, but I will give my life for your right to say it."

FYI none of the people you cited ever said that. This is a 1906 quote by Evelyn Beatrice Hall that has been misattributed to Voltaire.