I just tell myself that Starbinger was a lying sack of shit and is trying to emotionally manipulate me, but even if Starbinger is telling the truth (it's a fucking Reaper; of course it's trying to manipulate you, that's all they ever do), then it's the cost of a synthetic race verses literally everything else in the galaxy. A race that has on two occasions gone over to the Reapers and almost helped usher in the extinction. 

I love the geth and all, but it was no a hard choice. Sucks about EDI, but what's one life weighed against trillions? I set out to kill the Reapers from day one, I never wavered.