i thought about this in the past. the danger is centralized banning.
Discussion
The relay is accountable in this case, if i broadcast a note that censors a legitimate user there could be a public investigation and people would no longer trust my ip ban lists. Still tied to trust and reputation.
if a legit user and a spammer uses the same vpn, the legit user will be banned in more places than 1 relay
VPN users should probably not be using public relays, vpns will likely banned eventually due to spammers
Total transparency of relay filters helps address this because everyone involved has access to the same information.
Relay operators are not trying to suppress information without others knowing.