"But but but my favorite politician is not an orange racist fascist Nazi piece of shit", you'll probably say, but that doesn't matter. Imagine him being silenced anyway, because "Freedom of Speech !== Entitlement to a Platform", and the platform owners might suddenly decide that it is in their political interest to silence their political opponents.
Would you still honestly think that it is perfectly fine?
I'm not overly concerned since politician I support don't encourage their supporters to attack democratic institutions.
Trump being held to the same rules as everyone else[0] by a private party despite being a politician is basically the OPPOSITE of the government having so much power that even private parties will silence people the government doesn't like. So yes, I think it's VITALLY important to protect the rights of private Americans to NOT have to be mouthpieces for the government if they disagree.
[0] well, actually, he's still getting some kid gloves, but it's an improvement
1) there's the facist counter-argument "you shouldn't be able to silence the government," where the government having the ability to force me to repeat what they say scares me more than a company saying "I won't republish that"
2) there's this one, the "what if it was your favored politician"; this is pretty old news; not everything every politican says is published in every news outlet, editorial selection is as old as time, and we have to hope that there is enough competition in the market that things that resonate with lots of people find publishers (if anything, right now we seem to be suffering from being way beyond this, where we even have a lot of publishers for straight garbage nonsense). But this particular instance is an extra-weak-sauce one: nobody NEEDS twitter. Especially not the president!
3) and there's another angle where I think it's important that people act in line with their beliefs, not just with their wallets or their ad view counts, in order to preserve our democracy. There will always be bad actors. Trump is a bad actor. We can't simply throw up our hands and say "we have to accept all the bad actors because we might not always get it 100% right if we try to fight the bad actors." That supposed cure - doing nothing - is worse than the disease!
"Is this person a dangerous nutjob who cares more about their own power than the health of the country" is one of those things that affects which politicians I support, so I'm not TERRIBLY worried about politicians I support falling into this particular trap. Since I believe this is an exceptional moment, I think exceptional action is warranted and am less concerned with supposed precedent. Twitter and Facebook spent 5 years being huge enablers for Trump, even though they never liked his politics, after all, going back to the start of his campaign. Clearly they're willing to tolerate a LOT.
For now, the situation plays into your liking, because you think 'Trump is a bad actor'. But what would you sing when you'll be supporting the bad actor?
Simple example: Russian opposition is considered 'bad actors' in Russia by privately owned (by friends of Putin) tech giants, and is silenced on local social media.
Imagine a world where the online speech is shaped to the liking of a platform owner. It will logically lead to winning elections and forming government by the side supported by such platform, which will of course stay private to legally censor anti-government speech, which, in turn, will make replacement of said government nearly impossible via elections. If you don't see any problems with that, well, I rest my case.
I'd sign up for their mailing list.