They sided with McG because his ideals lined up closest with Orga's and because they themselves were very naive. Through most of season 1 they run on the concept of strength is might and a lot of their plans lived or died by Mikazuki's abilities. Naze was the guy who could change the dynamic, because he was a far more politically savvy guy who didn't run on just ideals. However, they got rid of him in a rather dumb way, but had he stuck around he would have just told Orga to stop being dumb. So they kinda put themselves in a corner with him being around. Orga saw the power of the Barbatos first hand so him being seduced by McG's dumb plan sort of makes sense.
We kinda see throughout the show that Orga is charismatic and will get people to follow him, his decisionmaking is the problem because he can't handle the stronger politicians. Once you cut off all of his good support then he was f***ed. Heck losing Biscuit really screwed them over, because he's another voice that would have gotten them to back off siding with McG.
Had this been a show like Code Geass or Seed or any other mecha show featuring a single overpowered unit, then yeah support him. Removing beam weapons was kind of a giveaway that you wouldn't be able to wave clear armies though. In fact, this show completely s***s on the idea of a chosen one. No Newtypes or any of that bulls***.
Removing beam weapons was a huge giveaway, but I was in the mindset of Turn A Gundam which also dealt with a legendary Gundam that brought about the current situation. I seriously thought nanomachines and a way to control Mobile Armors was a feature from older Gundams because I don't really see how they could have beaten armies of Mobile Armor with just melee weapons. Kinda inconsistent world building if you ask me! Even though I didn't like Turn A Gundam as a "Gundam" show I respected that the world building was consistent. You never see Turn A do crazy things but there were hints of its potential and they showed crazy stuff like self regeneration to give you an idea of the scope of power of a "legendary" Gundam.
And yea Orga crumbled magnificently after Biscuit died and he realized his responsibility as the leader. Naze should have never died though >_> was really dumb way of taking him away. I was also kinda frustrated that Kudelia was relegated to doing nothing after they propped her up as this war maiden of hope, like Jeanne. I completely had no problem with the ending, it was bittersweet. The reality of it was very powerful, you can't change the world by force to fit yourself into it, you have to work within the confines of the system and bring change that way. ---