oppose nazis

I mean, apparently that's a lot to ask in today's world, so your SO isn't wrong, but having a kid for that purpose is ethically questionable, and cruel as fuck to the individual kid.

"Sorry lil Timmy, your world is absolutely FUCKED but you've been chosen as a bucket of water to throw at the wild fire... good luck!"

The idea of having a kid is just mean. Or at least whipping one up from scratch is - adopting and raising the kid to be a decent person is the best case scenario here, but that's obviously a gargantuan undertaking that very few (absolute badass) people are willing and able to do.