Unquestionably the single-child policy. Not only would any woman who got pregnant after having her first child effectively be pressured into, if not outright forced to, have an abortion but the culture highly valued male heirs since they could 'continue the bloodline'. So if you/your wife got pregnant and it was a little girl in there... There's a reason there's more men than women in China.
Conversely in Arabia at that time women had very few rights and were often treated as being subservient to men with a religion that was outright hostile to the notion. If a wife got pregnant then got an abortion she'd probably have been severely punished if not outright killed and even simply miscarrying the baby (naturally or not) could result in public shaming.
I don't know what the views of the various NA tribes were on abortion, especially since there were a multitude of them so trying to condense them down into a single culture would be hilariously short-sighted, but they were not technologically advanced (especially in areas of medicine) and had small, tribal, populations. I would expect that every child would have been considered extremely precious and intentional abortion, if it happened, was probably extremely risky at best. Especially since I wouldn't be shocked if every child was considered precious due to small population sizes.
You can't go around and assume every culture had the same views and everything. Cause that's not how it was. Various religious, societal, population, technological, and resource-al? factors existed that would change how every culture would perceive it and there would be a lot of women who would be shunned into fear.
For every Rome (where we know there were a lot of contracepts used, we've found 'baby dumps', and I know of no taboos) there is a One-Child Policy China. It's a spectrum. I suspect that, in the future, there will be a culture that will see an abortion as being no worse than turning a computer off and on again or even possibly encouraging an abortion if the child lacks certain genetic traits.
Thanks for sharing your thoughts. I would absolutely only encourage abortion when necessary, and I think that the majority of society, even those that support it do treat it that way. There will of course be those that 'abuse' the system, but they are a statistical minority.
I stand with you against the concept of utilizing abortion for eugenics. However, there are many countries with far more permissive abortion laws that do not in any way practice eugenics. There are some that have of course (Sweden).