Objectively people with autism will have a harder life because of extra struggles. (Not that you can't have a good life, but you have a higher chance of struggling). The antinatalism movement is not about "improving the gene pool" or related to eugenicist ideals like you are implying, it is about reducing suffering. And the extreme conclusion is that the only certain way to reduce suffering is to stop breeding. (And not having children is not the same as some selective culling like you are implying is the 'spirit' of the post)

This isn't about exterminating autistic people, if the couple had adopted 3 autistic kids the op likely would not have had an issue. The op is pointing out how the desire to have "biological" children led to them doing a procedure that increased the likelyhood of having more than one child, and increased the likelyhood of complications.

Maybe "ruined 3 lives" is harsh, but I don't see this as eugenicist. It is standard antinatalism "having multiple children is bad when you could have adopted but your drive for 'blood children' led to this and they will now have a statistically more difficult life than their peers so you likely increased the net suffering in society out of selfishness"