If grandma's house could magically bleep the f word, then it would be the same thing
It's not about the f-word.
It's about the attitude that, when grandma says "hey, please don't trigger the magic bleep device in my hearing aid", telling her to fuck off because you can act however you want to act. If that's your attitude, you don't belong at grandma's house. That's not an attempt to be a part of the community, but a disruptive asshole, and grandma doesn't want that.
banning for petty shit is rude
I don't consider a ban for "responding rudely to moderator requests to tone it down" petty. It's toxic behavior.
I'm not a witness to the behind-the-scenes stuff with sigma. But I have been a witness to more than one behind-the-scenes event, and I've been impressed with their moderator staff. They do a pretty good job. The only people I've seen upset with them are Diedel and sigma, both of whom are known around the community for getting into trouble. So my assumption that they're not being petty or overprotective is based on quite a bit of evidence both of how they handle conflict (polite requests first; bans only as a result of being rude to them in response to those requests, and not a hint of pride), and how the people who get upset with them have handled conflict in the past (being dicks in response to polite requests).
What evidence do you have otherwise? You've got somebody you already know to be a "racist cussing ... jerk", somebody who regularly makes violent comments and throws temper tantrums on this board, who can't actually explain his complaint against them but has said vague things like "They talk to me as the chief of a subordinate" and "totalitarian corporate style". You might think the racist jerk is interesting, but that doesn't mean you should believe him when he claims they're at fault.