Taking away voting overall harms at a more massive level

Debatable. I think that most people want a tyrant as a ruler, as long as that tyrant that does what they believe is just/fair. That's why Trump cultists support Trump; he was hurting the people they wanted to hurt, and the rule of law was irrelevant to them. Hitler and Mussolini both gained power through elections, so I don't you can safely say that voting is always the lesser of two evils.

Likewise, dictators aren't necessarily harmful, although they often are. But it's not requirement. You could argue that it would be authoritarian to forbid people from deadnaming people, using racial slurs, or otherwise being assholes, and it would be. But it would be pursuant to a greater good, i.e., letting marginalized people feel safe(r).

In the US, we DO have laws that regulate speech already to a degree where mass harm

Not really. The 'fire in a crowded theater' is a myth, and it was a non-binding opinion that supported the idea that opposition to the draft (in WWI) was not protected speech. That decision was largely overturned by Brandenburg; the superceding decision said that speech was not lawful if it incited to imminent unlawful action. Lying for political gain is absolutely covered by 1A rights; look at George Santos. He's going to get in trouble for fraud and campaign finance violations, not all of the lies he told to get elected. Or MJT, the pedophile Matt Gaetz, Barbie Boebert, etc.

Fraud is illegal. Defamation (slander, libel) are covered under tort law, and are not criminal. Keep in mind that all the harmful things repeated by Fox talking heads about the election and Dominion Voting Systems was not criminal, despite the harms they did to society; that's why it required a law suit instead of DoJ involvement.

Obscenity is illegal presumably because the creation of obscene materials requires real harm being done to someone or some thing. (Although there was the case of Boiled Angel, but that was likely a loss for the artist because he couldn't afford to fight it in right-wing courts.)

Calling someone the “n-word” is a great way to lose your job, get punched, etc.

You've just hit the critical distinction. It's legal to call someone a racial slur, but it's not socially acceptable. (Nor should it be!) My workplace can absolutely tell me that I can't carry a gun when I'm on the job, and if I violate that rule, they'll fire me. If I pull a gun on someone while I'm on the job, I'll get fired, and if I'm not legally justified in doing so, I'll also lose my carry permit and be criminally prosecuted.

The distinction here is what the gov't can dictate, and what a private group can dictate. Facebook can censor your speech because--rightly or wrongly--they own the platform that you're using for speech; the gov't can not. (Fun fact: a gov't official using an official gov't account on Twitter or Facebook generally can't ban you from interacting with that page, because that would be gov't censorship.)