Can you imagine Harry killing Hermione because Voldemort threatened to plague all sentient life with one barely noticed dust speck each day for the rest of time? Can you imagine killing your own best friend/significant other/loved one to stop the powers of the Matrix from hitting 3^^^3 sentient beings with nearly inconsquential dust specks? Of course not. No. Snap decision.

My breaking point would be about 10 septillion people, which is far, far less... no, wait, that's for a single-event dust speck.

What's your definition of all sentient life? Are we talking Earth, observable universe, or what? What's 'the rest of time'?

3^^^3 is so large that claims on this order of magnitude are hard to judge. See Pascal's Muggle for a discussion of this.