I think defederation is an interesting element to Lemmy, but I wouldn't sweat too much over it. It's highly unlikely that any large instances are going to defederate from each other without a good reason. Namely NSFW content (so boobs don't show up on your "all" feed) and major political differences (so tankies and fascists and others with extreme political views don't bombard your communities). If you do want to subscribe to an instance with extreme political views or with boobs, then you'll probably need to have a few accounts for those different exceptions. And they can both be logged in at the same time. You can go to lemmy.world when you want regular content and lemmynsfw.com when you want boobs. But I really don't think you're going to feel defederation very much. Only in those exceptional cases. And there will always be instances that allow both the regular content and the nsfw/extreme content. If you disagree with your instance admins, you just need to find an instance that better matches what you want to see.

For what it's worth, lemmy.world seems pretty committed to not defederating. They haven't defederated from lemmygrad.ml (communist lemmy) like many other instances have. The only instance they've blocked explicitly approves of people posting loli (underage anime porn), which is pretty damming.