grregg said:
Well, Saren can prove that organics are useful in destroying other organics. Which Reapers probably know, that's why they developed the indoctrination, right? So assuming that he helps them destroy the current batch of advanced civiclizations, what exactly is his usefulness at that point? Zero, right? What can he possible provide to the Reapers?
Perhaps to extract resources for them. Indoctrination, in his mind, wouldn't be an issue if he proves that organics can willingly help them and be much more efficient at it.
It's a warped logic, there is no doubt about it, that was manipulated by Sovereign. But it's not completely idiotic.
What I will say is that the details of Sovereign's manipulation are not shown. Perhaps Sovereign told him how he can organics can be useful to them if they submit.
EDIT: also I don't think Saren knew that other organics were used by the Reapers.
He most likely did not know of the Collectors.
1. They invade straight up, relying on the element of surprise, the Geth fleet and Saren's infiltration of Citadel as a Spectre, or
And how do you propose he takes over the citadel controls, and defend it before other Specters or C-Sec stop him?
He needed Geth with him in the Citadel and the COnduit was the best chance to warp an army of Geth right near the presidium.
If Saren fails to open the arms, or keep them closed while Sovereign was inside, the plan would fail.
EDIT: keep in mind that Sovereign had been planning this for a long time.
The plan was enacted only after Sovereign knew that all the pieces were ready, and he knew that Saren would be the best man for the job.