[Crazy Eddie]

^ Basically. Starchild's reasoning is plainly absurd, since the situation with the Geth indicates the Reapers themselves are the biggest cause of conflict between organics and synthetics. When you think of it that way he's launching this huge genocidal war as a bit of circular logic: "The New kid will always get beaten up by the bully, so I'm going to go and beat up the new kid so the bully won't have a chance to clobber him."

...we get the refuse/fuckyou ending and it's pretty clear that Starchild is just Harbinger trying to cut a deal with Shepard. This actually confirms my earlier theory about the nature of sacrifice/unification, in which case Harbinger HIMSELF is the one imposing this solution. In essence, the Cycle was always meant to be a temporary solution, not a solution to organics vs. synthetics, but a solution to Reapers vs. Everyone. Left to their own devices, the Reapers would just as soon pillage the entire galaxy and kill everything in it, but someone -- probably Harbinger -- redirected the Reapers to only focus on technologically advanced races while leaving the others alone.

When you consider that both the citadel and the mass relays were originally created by the reapers, and when you consider that the crucible is designed to use both of these as part of the solution, then you're forced to acknowledge the very strong possibility that the crucible is ALSO a reaper invention, probably created by Harbinger as a way to force an eventual end to the cycle. Harbinger couldn't build the Crucible himself, the other Reapers wouldn't have allowed it; he also can't USE the Crucible, since both the control pulse and the synthesis wave would probably fry his synthetic brain before he had a chance to finish the job. He needs someone who has not been indoctrinated and who otherwise wouldn't be destroyed by that radiation until it's had time to take effect -- an organic, in other words, and not just any organic would do, it would have to be someone with a ridiculously strong will and a unique enough understanding of the situation to make an informed choice. That also finally explains why shooting the power conduit triggers the (temporary, I'll bet) destruction of the Reapers: the Crucible was designed by Harbinger to primarily affect the Reapers, and blowing up that power conduit causes it to OVERLOAD them instead of control/pacify them. Harbinger seems to prefer the Synthesis solution; we already knew this about the Starchild, but now we can understand WHY: he doesn't want to destroy all organic life, but he doesn't want to destroy the Reapers either.

Circumstantial evidence for this one: when Harbinger descends to Earth to wipe out Hammer, he leaves Shepard alive with only a token force of troops to keep him away from the beam. Supposing that Harbinger knew what was going on in London -- and dropping out of orbit like that, he MUST have -- then it means he didn't go down there to keep Shepard from getting to the Citadel. He went down there to make sure the NOBODY ELSE did. And the Illusive Man, whether he knew it or not, was tasked with the sole job of making sure nobody but Shepard could make it to the Crucible to make that crucial choice. Thus the Illusive Man makes no real attempt to kill Shepard and either finishes himself off or makes it real easy for Shepard to kill him, but only AFTER Anderson is effectively out of the way.