He said that he should protect the existence of Organic life from Synthetics. Why should he care organic life? More importantly, Why should he care 'the continuous existence of Organics' even if he destroyed countless Organics during past billions of years? Why shouldn't he allow Synthetic's dominance over Organics? Is he God? If so, Why should he discriminate Synthetics? Thousands of Organics species extincted during one cycle even before Reaper's genocide. Why did he allow some Organics to dominate other Organics but not allow Synthetics to dominate Organics? (Of course, Reaper used Synthetics to destroy Organics during their harvesting. For example, Reaper used Geth, Zha'til. But let's forget it for a minute. Again, Catalyst is really the worst hypocrite) Only possible motivation for Catalyst : During harvesting, Reaper absorbed Organics knowledge, genetic potentials, technology and so on, according to Catalysts and Vigil => Thus, Organics were Reaper's food. So, they should protect their food resource from other Synthetics. In other word, they just tried to monopolize their food resource. Any better idea? It seems clear that word of Catalyst doesn't make any sense if we should take it at face value. Catalyst just pretends to 'help' Organics.