…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
60 minutes did a piece about this decades ago. I was talking about it with an older woman at church years later. He first thought was ‘that is not good, it will mean war with too many men’.
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.
If women keep killing baby women, eventually there will be no more women...
People who believe in abortions basically have a moral compass that goes like this: "abortions are good if they benefit me and bad if they don't benefit me". Most pro-choice women are feminists thus abortions are good if they are done for them personally but bad if they are done in a manner that makes women appear to have less value than men or doesn't push their egalitarian agenda.
You're not going to beat them with this "logic" because these people are in fact adhering to their moral beliefs.
You can't convince most people on the Internet that they are wrong, but this isn't for that purpose, it's to discredit them on a discussion so that moderate third parties reading can reflect on how wrong the pro-abortion position is.