Both sides present the most agreeable arguments for their position, while publicly omitting other motives, while simultaneously highlighting the least agreeable motives of their opponents and omitting or flat out denying their more agreeable motives.
I don't mind being candid (not least because I am not an important person and this is not an important discussion, the stakes are low so there is no pressing need to lie), so I'll say one of the quiet parts out loud for the side I mainly sit on: I think there is plausible social benifit to aborting pregnancies caused by rapists. Not only because rapists might carry genes for aggression, but also because rape circumvents the valuable social/physical fitness selection which women normally perform when choosing who to have babies with. Pro-choice advocates will almost never admit to believing anything like this, because it essentially validates the criticism antiabortion advocates have, that their opponents are eugenicists. To be clear, many pro-choice advocates aren't, and I don't think this particular argument would make or break the debate (it doesn't for me), but it is a potential source of contention pro-choice people might have with my artificial womb proposal.