but if everyone had eight kids it'd probably be a problem.
Yea no shit, but that's a stupid hypothetical that is most likely not going to ever happen, so it isn't even worth considering.
What would you think if a democracy decided no more than two? How would that sit with you?
I'd tell those people to go fuck themselves and if they force my partner to have an abortion against their will just because we went over their arbitrary limit, that I did not agree to, then there's gonna be a fucking fight for our right to have a child if we so wish.
What part of "no one should have authority over the reproductive rights of others" is unclear?