Unless you're advocating for P2P chat, I don't see how it's any different for open source solutions. At some point you have to trust the people hosting the centralized servers, OSS or proprietary.
Of course, we need decentralized solution at minimum, distributed at best.
Also about trust: I can trust a bit certain kind of paid hosting/services, for instance companies that are in my country under my country law can be trusted in the sense that I have a certain kind of legal protection and a clear signed contract. It does not stop them do thing I can't know with my data but I have few options. Against services hosted elsewhere in the world with "not-real-contracts" and zero formal fee my possibility of action is essentially ZERO so I can't even being protected by my country's law.
Also about trust: I can trust a bit certain kind of paid hosting/services, for instance companies that are in my country under my country law can be trusted in the sense that I have a certain kind of legal protection and a clear signed contract. It does not stop them do thing I can't know with my data but I have few options. Against services hosted elsewhere in the world with "not-real-contracts" and zero formal fee my possibility of action is essentially ZERO so I can't even being protected by my country's law.