What happens if it should come to pass is that users will need to decide whether they like it like that, or move to a third party instance that doesn't block either one or only block the one they want blocked.
And the prospect of a user exodus (for a decision either way) is an incentive for admins to pay attention to what their users actually wants. To me that's just fine (though I'd like improvements to the user migration functionality to make this process even easier).
I could worry about this, or I can worry about Musk's whims. On Mastodon I can move elsewhere (and did; where I started was fine, but I'm now on my own instance because I like having more control). On Twitter, there's no recourse. As such I'll take those future hypotheticals over what's happening to Twitter any day.
Look at how many controversies there have been about whether Twitter should or shouldn’t ban some controversial figure (everyone from Donald Trump to J K Rowling). What happens if Mastodon gets similar controversies, and then big Mastodon server operators disagree among themselves about how to respond, and then block each other’s servers out of that disagreement? Nobody can say it can’t happen, I can’t see any guardrails to prevent such splits. If anything, Mastodon’s community seems to be full of people who think that Twitter (whether pre or post Musk) is insufficiently moderated and not banning enough people, which seems to make such a development only more likely