Some spoilers from ME3 and FFX here:
So I'm reading up on the Catalyst, and he explains (apparently) that the first Reaper was created by an organic race that was getting absolutely decimated by a synthetic race, and this was essentially a last resort to preserve themselves in another alternate form, subscribing to a dogmatic approach that "all synthetic life will destroy organic life" and operate solely on this basis for justifying their actions.
So.
The Reapers are essentially Sin?
--
TheRock ~ Slow dramatic zoom-pan. Doesn't phase the hooded man.
"You have issues." - MWC. Pot. Kettle.