User blog comment:The Milkman/Shades of Purple/@comment-5287758-20120930050555/@comment-24174486-20121002232609

"How can it differentiate Synthetic and Organic life?"

Perhaps it is made to specifically target synthetic systems. As the Reapers are partly synthetic, this would be a way to eliminate the Reapers without endangering organic life, but would also cause the destruction of synthetic life as well. It's not the first time Mass Effect has had something that harms one form of life and not another: there's the electromagnetic pulse in ME2 that you have to escape from if you choose to destroy the heretic geth, as Legion tells you that it will damage unshielded organic matter.