Might I suggest doing a tag search on here for "foundations" and "lessons" there are some great threads that indicate ideas on how to approach poly in a healthy way. Compassion is important for sure, as is honest open communication, respect for others and your self, and compassions cousin if you will, consideration. All can be found in great details if you look around a bit.
If you intend to debate I suggest reading around a bit too. You have said in your post, before editing that you "have some major disagreements on key aspects of what "polyamory" really is. I will probably at some point criticize and debate every argument used to justify it as somehow more evolved, or healthier a lifestyle choice." ...Most off us have debated it all pretty much and while a good debate is awesome, I am not big on repeating myself when there are threads already that address the issues. Please feel free to add questions or comments where ever you see fit on the threads you find. Thanks.
I hear that this is all painful and difficult. Your whole worlds have been turned up side down it seems. I would suggest slowing down, taking a breath and keep commuinicating. You seem to be on the right track though... With some boundary negotiation and setting, things will settle with time and patience I should think.