"Permitted" is a strong word for activity enabled by a protocol. It implies some moral acceptance from the ones who designed the tool. I think a better word would be "possible". Similar to how e-mail makes it possible to send all kinds of content.

This is why free speech is so hard to maintain. There are so many cases where you want to ban or censor something obviously repugnant, but once the power is created to do so, it will be abused, probably as soon as someone you don't like is now in charge.

It really isn't - the cheese pizza lover can make their own instance

“Cheese pizza” is banned by law in most countries, so it won't be “permitted” either way.

That content is prohibited by law anyway so it's not really relevant to internet moderation standards anyway.