We need anti-abuse systems, but it's impossible for instance blocklists to scale to the size the fediverse needs to grow. It's mostly working for now but won't long term.
Easy demonstration: imagine everyone self hosts, and that self hosting becomes trivial. Everyone agrees that's a good goal, right? (If you don't, maybe you don't really want the fediverse?)
In that case, it's trivial to make new instances, meaning already-overloaded administrators will be overwhelmed with "swatting flies".