That's simply untrue, speaking as the admin of a smaller instance. There are blocklists but they are entirely up to yourself to implement. I myself only implement rules to completely block far-right instances or "free speech" instances, those tend to cover almost 99% of content that would be frankly illegal for me to federate. The rest is a few japanese and sex-positive instances, which are only media-blocked, so they still federate but I don't allow their media on my server, which I think is an acceptable compromise completely blocking it. And from talking to other people running instances, this is pretty much the norm for the fediverse, regardless of what the far-right instances want you to believe.
It just feel very weird to me that the word "fediverse" is thrown around like a universe, except it is a balance of not getting thrown out by not being the norm. Perhaps it is just me that has this fantasy of everyone being in one place, at least on the Internet, but jerks are jerks.
The Fediverse is simply a term for all of the instances. It's not entirely fragmented, there is certainly shared hosts between bubbles in the fediverse. Though I don't think this is an issue really; our own universe functions on the bubble principle as well and it makes fediverse a place that you can find an instance to be on without having to worry that your instance moderator will allow nazis to vent their garbage into your feed.
