User blog comment:Ygrain/EDI and the geth: their purpose in the story?/@comment-24174486-20120723182551/@comment-24174486-20120723202139

"The endings reflect the solution of the Catalyst's problem, whether real or imaginary, not the theme which constituted the rest of the series, which, IMHO, is bringing together diverse people for a common goal and finding strength even against impossible odds."

Not necessarily. The Catalyst itself tells you that Destroy would not be a lasting solution to its problem, that later generations would create new synthetics. Control does nothing to necessarily alter the balance between organic and synthetics. The only option that permanently alters the balance is the choice the Catalyst personally approves of, Synthesis. Regardless, each of the options have valid arguments for them that do not take the Catalyst's "problem" into consideration.

The Catalyst decides that the Reapers were a poor solution and assists Shepard in activating the Crucible because of the impossible odds that Shepard overcame, because Shepard managed to unite diverse people for a common goal, because Shepard managed to reach the Catalyst itself. Shepard wins over the creator of the Reapers by accomplishing the impossible.