I agree with your main point that the 1st amendment is a protection from the government.

Your friends, employers, sponsors, etc not wanting to associate with you for your speech is perfectly fine.

The tricky part is when it comes to government-funded and protected entities.

With colleges, with only a couple exceptions, they are institutions of state governments and/or receive direct federal money. So when a college says "you can't say that here" it is a government body limiting speech. I find that to be a problem.

Twitter and the other social media companies have a weirder entanglement. For them, it's the issue of platform vs publisher. They all claim they are mere platforms and are then protected by law from the liability of their users' speech. But when they censor their users' speech, they are editorializing and becoming publishers. As the situation stands now, they are having their cake and eating it too. I think they need to pick one side or the other and stick to it. Either they are platforms and do not police content or they are publishers and have all the regulations (positive and negative) of magazines, newspapers, and the rest.

This is actually one of the major motivations for creating talkingpoint.co. Using a blockchain social media system, users literally cannot be censored. We can prevent them from showing up on the website, but we have no ability to censor the blockchain.