If an instance defederates from another instance there’s nothing stopping a user who liked that instance that was defederated with from moving to, making an account on or just using (in the broadest sense) another instance which hasn’t defederated with the instance they like or that instance itself. I do this sometimes, I go on to another instance I don’t have an account on to see the content a defederated instance treats as acceptable and thus the culture it has.

That’s one reason I moved to the fediverse: so I could get rid of all of the content I didn’t want to see before I saw it. More typical social media like Meta, Twitter and Reddit all have a long history of failing to moderate against anti-trans hate, as with other types of hate, so I moved to the fediverse. One thing that stuck out as a major selling point to me at the time was a lack of an algorithm, meaning that everything I saw I saw because I searched for it, I subscribed to it, because it’s local or has been crossposted. Those latter two cases are the only real examples I can think of where a user is served content they didn’t actively search for, and even then they’re likely to be interested in it because an instance with a specific purpose, like lemmy.blahaj.zone or slrpnk.net, would only host communities that fit with the userbase’s interests.

One of the reasons I use lemmy.blahaj.zone as my instance, which Katy also uses, is because the admins do their best to weed out transphobia and that includes Threads because Meta has poor moderation. It’s already fairly well established practice to block or defederate from instances with poor moderation (sometimes including open registration) because they pose risks to an instance’s userbase. If my instance federated with Threads I would feel at risk from Threads users attacking my posts or my private messaging inbox, so I would leave. We have already seen “aggressive” or “troll-ish” behaviour like this from instances which are far smaller than Threads are.