Messaging relays can always be taken down, DDOS-ed, you name it.
Such actions can temporarily disrupt the network.
What is more important long term, that operating a relay costs money. That cost is not spread evenly across network users which can lead to actions that aim to fund relay operations in a way that can be not optimal to the network users.
This is why I'm more excited about Keet.io than #Nostr long term. #Keet team built p2p messaging app that don't require servers (including relays) to work. Other network participant can act as fragmented relays (using blind mirroring tech, video below), so the decentralized p2p network without servers can stay reliable without disruption.
Are you a dev interested in building 100% P2P apps using the same stack Keet does? Check out holepunch.to to find out more about this exciting technology.
https://video.nostr.build/9756504cc91346fb4d502b1f58289dd8ca3d31dd103113c1d66ad699fe31ad57.mp4