Wow, there's no way to comment on Saletan's blog posts instead of just his most recent Slate article? Anyway...
Sarah Hrdy has written some interesting things about infanticide in her recent book, Mothers and Others. I think there's more about it in Mother Nature (also by Hrdy), which I haven't read. (Yes, her name is Hrdy, not Hardy.) It seems that infanticide is fairly common (although also considered painful) in hunter-gatherer societies. Mothers look their babies over before deciding to keep them (although the decision is based as much on perceived levels of social support as on visible deformities), but once they decide to keep them, they don't later change their decision. Perhaps prenatal screening and access to abortion result in a reduction of infanticide? A lot of people consider the dangerous back-alley abortions that would result from a ban on abortion, but infanticide is not often mentioned (real infanticide, not "infanticide" as defined by some pro-lifers).
I doubt that, for someone who can kill an actual real-life baby, an ultrasound would make that person less likely to kill their baby once it becomes a baby. If they can deny that a baby sitting right in front of them, a baby who cries when it is injured or abandoned, has a moral claim on them, I doubt a grainy video of a developing embryo or fetus will sway their emotions. But maybe it will alert such a person to the urgency of making a decision to end the pregnancy while there's still time to do so. On the other hand, maybe the emotional impact of the ultrasound will make such a person dither further, retreat into denial about the pregnancy, and not terminate the pregnancy, making later infanticide more likely.
