I also think mainstream Mastodon is only left to far-left in the median, because far-right instances tend to be more of a pain in the ass to be around than far-left ones, and thus get themselves banned more often. If there were far-left instances running around posting memes "joking" that we should kill minorities, I'm confident they'd also get disconnected quickly.
Put another way, I don't recall ever disconnecting with an instance because of its users' opinions, unless those opinions were utterly vile to the point that I'm completely unwilling to hear "their side of the argument". Most blocks are due to bad behavior, not unsavory thought.