RCS is an open protocol, in fact it was developed with the GSM association https://en.wikipedia.org/wiki/Rich_Communication_Services
You seem to want every single reason to dislike anything Google has ever helped to make, rather than doing actual research into what some of these things are.
It's an open protocol but it's not an open system, just like SMS. You can't just set up your own RCS provider like you can with the web, email, IRC, etc. So it's at least a little misleading to call it "open".
So that explains what happened, it still doesn't excuse forcing it, without permission or notice, on people who are using an open protocol