[XorNot]

So again: if I have a comment section on my personal blog - can I remove abusive comments? Ban abusive users? Can HackerNews ban or downvote comments so they're not seen? Can TalkBack radio screen which callers it puts on the air?

You can write a law to do whatever you want, but the reason rights like freedom of association are enumerated is because things will go very, very wrong quickly when you undermine them. Freedom of speech is protection from government sanction for voicing your ideas, but freedom of association is protection of your being compelled to act due to the arbitrary desires of others.

> If you had a lemonade store, in a mall, and you were giving away free lemonade, but you refused to give away lemonade to black people, then you absolutely would get in trouble with the law.

No you wouldn't. You'd be in trouble if you ejected people from the premises on the basis of race, but there is no case-law which requires you to give away goods and services to anyone. But this comparison is completely irrelevant because "your opinions" are not a protected class, nor would they ever be.