The exact same argument can be made for the centralized services that Ethereum relies on. If Infura would serve incorrect or censored data, it only takes _one_ person to find out and the trust we have in them is also lost forever.
There is no fundamental difference between the trust placed in relaying services like Infura, and the trust placed in software supplier like Signal. Both companies/services are able to cheat or betray that trust in a way that regular users will not easily notice, but both of them are fully auditable by technical users. Since their whole business model relies on being a trustworthy service provider, it makes no sense for either of them to attempt to cheat, because they risk their entire reputation.
There is no fundamental difference between the trust placed in relaying services like Infura, and the trust placed in software supplier like Signal. Both companies/services are able to cheat or betray that trust in a way that regular users will not easily notice, but both of them are fully auditable by technical users. Since their whole business model relies on being a trustworthy service provider, it makes no sense for either of them to attempt to cheat, because they risk their entire reputation.