Slavery is widely and rightly regarded as among the worst of moral evils. Abortion is not. On the contrary: the latter is now celebrated in some circles. Why the difference? Why the difference when both are grave moral evils? 'Skin in the game' plays an explanatory role. Not the whole role, perhaps, but a major one.
No one in the West owns slaves or has an economic interest in them. There's no skin in the game. But everyone is naturally concupiscent. There's plenty of skin in that game both literally and figuratively. Add to the natural the social: Western societies do little or nothing to restrict, and quite a lot to facilitate, the pursuit of sexual gratification for its own sake. Now add to the social the technological: safe and reliable birth control and safe and reliable abortion. The resulting trifecta of mutually reinforcing factors has brought us to the current decadent and hedonistic pass.
It is easy to think clearly and disinterestedly about slavery and its immorality since we have no stake in it. There are no passions or interests to suborn the intellect. Denunciation of slavery and its real or imagined consequences such as 'institutional' or 'systemic' racism also allows one a cost-free way of displaying one's supposedly high moral status. One doesn't have to give up anything or do anything. One signals one's virtue by one's bien-pensant attitude. At most one will be called upon to mouth some politically correct pieties. One's 'thinking' merges easily with thoughtless groupthink.
To think clearly about the immorality of abortion on demand at any stage of fetal development for any reason, however, requires one courageously to cut against the grain of groupthink and to resist one's natural desire for unlimited sex without consequences.
For one whose mind is in the grip of the Zeitgeist and his loins in the grip of concupiscence, rational argument arrives too late.