They go into a black hole because Nostr is too small today and we're living with these public relays anyone can write. That situation cannot work if Nostr gets bigger, there will be too much spam. Many relays will be forced to close themselves only to users that meet a certain criteria (payment, relationship, content quality, PoW, etc), then once you have that it becomes in the interest of these relays to exclude people who aren't behaving well, therefore reporting them to the relays they use becomes a meaningful act.
https://pyramid.fiatjaf.com/ has a reports page where presumably I or other users can check if some bad actor got accidentally invite and remove them, for example (not that it has ever happened).
Anyway, the crucial part is that what can be bad behavior for me may not be for you, so my relay may only accept notes full of love and kindness, but yours may accept notes full of rage and sarcasm, and both are ok -- that brings us to the next step: if a user only wants to see love and kindness they should be able to configure their stuff to only see replies that come from my relay in some situations, for example.
How all of this works in practice I cannot say for sure, but I see zero centralization pressure in any of these steps.
