It's not discrimination to say "the message you just sent is green because it went over SMS (and now RCS) and we can't verify the E2E encryption, deliverability, etc like we can with iMessage".
I'm fortunately too old to ever have experienced this myself, but so I have to rely on others' observations for this.
That said, I wouldn't quite call it "discrimination" yet, but it's certainly uninformed, targeted at the wrong entity, and on top of that is at least a bit icky given the quite large difference in retail pricing of iPhone and Android smartphones.
The reality is just that people only install new apps if the preinstalled ones don't do the trick, or at least only if most of their friends already have too.
So in my view, the entire problem is that apparently no regulator has been considering it a problem for the better part of a decade that Apple is effectively running half of the country's communication infrastructure without being regulated anywhere close to the way landline or mobile carriers are from a competitive and interoperability point of view.
But this seems to already be changing; Apple definitely didn't implement RCS out of their strong desire for openness and interoperability. I just wish they'd picked a better protocol/system.
On the large scale, I agree. We have telecom regulations for good reasons.