…Killing two birds with one stone.
The question is: Do you agree that women in China should be able to abort even if they only choose to abort women (or XX cromosomed being or whatever they call it)?
if they disagree then point out "how come if you are pro-abortion" and "so if the woman's decision is biased towards women you are against abortions?", and stuff like that.
If they agree (because it's their body, their choice): So are you okay with women discriminating against other women on the sole basis of being a woman?
If they say yes, you won the internet. Some say it without even realizing what they just said.
If they say no, they will swirl around the idea that either "the fetus is not alive" or "it's part of her body" or whatever dumb idea. You just circle back to the concrete example of China: Even after the baby was born, some just straight abandoned them or killed them, so are you okay with the right of the mother to "not have a baby".
Inform yourselves pedes for the ongoing meme war, here's a starter: https://www.npr.org/2016/02/01/465124337/how-chinas-one-child-policy-led-to-forced-abortions-30-million-bachelors
I doubt reason can reach them… "Then we should just abort all males, they're toxic anyway, and stop being so racist with China" or something like that.
When you discuss with some radical on the internet you aren't engaged with them to win the argument, you are so you can discredit their position so non-radicals can see it's morally wrong and false.