Did you read my reply? Again, the ways to express numbers can be different, but the numbers themselves can not. Aliens in a different universe may use a different way to denote the number 3, but no matter how they denote it, it is not between 1 and 2.
They only post in their own communities on their own instance. You will only see their posts if you’re subscribed to those communities or browse All Why would you consider that spam?
E-mail is also a federated protocol. Imagine if every time you wanted to send an e-mail, you had to check whether your provider likes the recipient’s provider and if not, create an account at the recipient’s provider (if that’s even possible).
Yes, and thus you have one giant mega community in which every bigot can access anyone and everyone else.
How would removing defederation result in a situation where “every bigot can access anyone and everyone else” if user-level instance blocking was still a thing?