But I believe the issue that RC is talking about is that the control is in the hands of the admins instead of the individual in Mastodon.
It allows something like GMail admins blocking their users to send/receive messages from HotMail, and then your only solution would be to create a second account in some other provider that doesn't block HotMail.
Control is in the hands of an admin, but not any particular admin, and that admin might be you.
A more apt comparison than Gmail/Hotmail would be if one of the e-mail providers was whitesupremacy.net. Or, we-allow-white-supremacy.net. The admin of my we-dont-like-white-supremacy.net e-mail provider might choose to block it, based on the content it sends out. Anyone on that provider is welcome to choose another one if they wish to e-mail me. But if it is important enough to them to stay where they are, then they will remain blocked.
Long story short, if you don't trust the admin, don't sign up for the Mastodon instance. I agree that there needs to be some work on porting accounts from one instance to another seamlessly, though.
And communities should be instance independent the same way mailing list works.
Personally, I don't consider a Jewish person being spammed with images telling them to get in an oven "curated bubble piercing". Same with lynching threats against black people and rape threats against women.
All of these things happen on Twitter daily. And very often, when these posts are reported, Twitter comes back and says "we found no problem". You might not experience this kind of abuse, that does not mean it does not exist.