corpselover wrote...
And yet the ultimate manifestation of synthetic life has come to the determination that organic life needs to be preserved. That alone makes it hard for me to accept that synthetic life is destined to determine that all organic life needs to be destroyed.
The only thing I can really say to that is that the Reapers are a combination of Synthetic and Organic components; they are hybrids. Whether this was a result of synthetics and organics willingfully combining (as in the Synthesis ending) or an Organic race deciding that the only way to combat synthetics is to become part synthetic themselves is unknown. They do not, however, represent the ultimate manifestation of (purely) synthetic life.
What intrigues me, now that I think about it, is who gains and who loses in the Synthesis ending. Synthetics are technically superior, so adding a biological component seems unnecessary (i.e. something that doesn't have easily repaired components, that isn't interchangabel, that requires sustenance etc.). On the other hand, organics potentially stand to gain faster intellects, and wider connections to other individuals (among other things). By becoming part synthetic, organics A) have improved capabilities and

have no reason to create purely synthetic beings that they could come into conflict with.
Therefore, there is a possibility that the Reapers are the pinnacle of Organic evolution, not Synthetic as you propose. Since the Catalyst did not have this capability untill the creation of the Crucible (as cheesy as that is), it was forced to strike a balance between Organic and Synthetic. With the Synthesis ending, there is no need for the Reapers because the potential threat of synthetics destroying organics no longer exists now that such distinctions no longer exist.
Also, to nuance your last point, Synthetics are not necessarily the ones destined to start the conflict. Organic's fear of Synthetics could spark the conflict as well (which the Synthetics would assuredly end).