AgentPierce
Mad science FTW!
So they wouldn't betray him at the crucial moment, of course. Especially after losing Saturn's loyalty.
But Saturn stopped being loyal to him only after the Spear Pillar event, so that makes no sense. Saturn tells you when you come to him later "I heard about you and what happened at the Spear Pillar." He only learned of Cyrus' desire for a spirit-less world due to hearing about him making a speech about it at the Spear Pillar. Mars and Jupiter most likely just found out about it then as well, when he was making the speech; we just didn't see how they reacted. All we know is, whether or not they find the idea of a spirit-less world agreeable, they're still loyal to Cyrus on a personal level, as they're devoted to finding him after he disappears.
And really, it makes little sense for Cyrus to tell them about the truth of his desires. That would require trust, and Cyrus likely looks down upon trust as weakness. I think it's obvious that in all iterations (games, anime, mangas), Cyrus was the only one aware of what would really happen. Everyone else thought that the world would be changed, or knew that the world would be destroyed to pave way for a new one, but only Cyrus knew just how that new world would be: a world with no emotion, willpower, or knowledge.
Oh golly yes that would have been fantastic. Not only discarded but used as a test subject!
You know what would have been interesting, building off the "nobody likes Charon yet somehow he has tons of minions" angle--if they'd been under mind control as well. It would have been fascinating.
Better yet, Rotom could have been used to power whatever device Charon used to mind-control his minions! Damn it, Ihara really should have had the Platinum arc be 5 volumes (like the DP arc) so that he could expand on the plot alot more.