> My point is nobody has any problem with the myriad of other messaging platforms that are completely closed
That's entirely wrong. A lot of people are angry with every closed messaging platform, which is why people are still maintaining the matrix bridges to Discord, WhatsApp, Facebook Messenger and Signal, all of which are still a cat-and-mouse game, violating the ToS of those services.
Those bridges are actually what Beeper Cloud, their primary product, later was also based on.
And these bridges originally are based on the libpurple backends for Slack, Teams, Facebook Messenger, WhatsApp, Signal, AIM, ICQ, Google Chat, Skype, etc, all of which were created through reverse engineering.
So, yeah, fuck those closed services, messages want to be free, and enough people will care that we'll break all of those services.