It’d be one thing if X didn’t actively promote disinformation but they are doing that. They’re picking what and who to promote via their algorithm.

That’s the argument being revisited in US courts right now. If you choose to promote something, you are doing the editorializing and shouldn’t be protected under Section 230. And with how much a certain party hates the whole section, it’s likely to get struck or limited if it ever reaches the Supreme Court. That irony would be lovely.

If they had a hands-off approach to free speech (like any given Mastodon instance) I’d agree with you.

Just to be clear, Mastodon doesn’t have “hands-off approach to free speech”. Each instance has clear rules around what they allow and don’t allow. Just the federated nature of it prevents censorship, so all opinions can be heard.