Even if what you’re doing is making open source software that in theory benefits everyone, not just google?

FWIW I agree with you. I wouldn’t and couldn’t either but I have friends who do, on stuff like security, and I still haven’t worked out how to feel about it.

& re: countries: in some sense I am contributing. my taxes pay their armies

When you work for Google, you normalize working for organizations that directly contributes to making the world a fucked up place, even if you are just writing some open source(a corporate term, by the way). You are normalizing working for Google.

And regarding countries, this is a silly argument. You are forced to pay taxes to the nation you are living in.