User blog comment:LDR/Possible Reaper Motive/@comment-3268946-20120226062522

This just gives credence to what I thought the Reapers motives were: they believe themselves to to the epitome of what life is, free from all possible weakness. They believe themselves to be, in a word, gods. When they see a species reach this apex of civilization, where they have mastery over mass effect fields, they believe that this species' achievements should be rewarded with what they believe is the ultimate gift: the "apotheosis" of that species to a Reaper. They believe what they are doing is not only right, but necessary for other species to be given the same chance. But because organics treasure their own individual lives so much, the Reapers motives are truly beyond our comprehension in terms of morality.

Thats what I believe the Reapers motives are, anyway. Most of my reasoning for this comes from in-game conversations, such as Dr. Kenson, Sovereign, and Legion, among others.