You're stepping well outside the bounds of your analogy. Incoming email is like a social media feed, hence the comparison. It fails when you compare things like shadowbanning with spam, as I pointed out.

Going out onto the "dark corners" of the internet though, that would be equivalent, perhaps, to signing up for an equivalent email provider without a spam filter?

Nope, that doesn't work. Hard to tell what you could mean other than "my initial analogy didn't work so I'm going to move the goalposts".

Promoting hate speech to be published in the same spots as not hate speech because "free speech" is similar to putting the spam in with the regular mail. You're causing damage and actually preventing "free speech" because your speech incites action against those who they are speaking against. It also simply drowns out regular speech. Nobody wants to use a platform that has child porn or white supremacists plotting murder.