You know, a centralized system is not immune to any of the issues you are listing here.
Whether your mistakes can be deleted is up to the operator. They can even lead you to believe your content was deleted, while reporting it to the authorities.
> What if you post a communication system with encryption methods, but then the government passes a law that is criminal
Did you post it while it was legal to do so? Yes. Are you distributing it after it was deemed illegal? No. If you are in a country with a fair justice system, you wouldn't have to worry. If you are in a country without one, they will find a much easier way to get you anyway.
Whether your mistakes can be deleted is up to the operator. They can even lead you to believe your content was deleted, while reporting it to the authorities.
> What if you post a communication system with encryption methods, but then the government passes a law that is criminal
Did you post it while it was legal to do so? Yes. Are you distributing it after it was deemed illegal? No. If you are in a country with a fair justice system, you wouldn't have to worry. If you are in a country without one, they will find a much easier way to get you anyway.