Their own deformed child? Probably more than their normal child. Someone else they know personally? Maybe about the same as a normal person they know. But not an abstract deformed child or one developing in its mother's body. That's where the mother will have to be encouraged to empathize. That's also why the government and all other agencies must stay out of any decisions.
Another race? Doubtful if he/she is purely an abstraction. But there are real people of other races who I know and empathize with as much as those of my own race.
Human beings on the "enemy" side? This is difficult. You can immediately identify with war victims on your own side especially when you know them. Even if you just read about them in detail (e.g. reading about 9/11 victims) it is amazing how much empathy you can feel. Unfortunately war tends to translate that positive emotion into negative ones like anger. Emotions run high and often get expressed negatively.
Before the recent war I criticized some obvious anti-Iraq propaganda here and was told by a veteran to "STFU", that the propaganda was needed to whip up morale in the troops. Maybe he was right, but I'm not sure his prescription is useful beyond the those actually doing the fighting.
Anyway, that's off topic, but my answer in the abortion debate is that empathy extends from the object out to the empathizers. Mothers should be helped to be made aware of their unborn child and it's humanity in whatever ways are possible. Others can look at a picture or a thousand words. I believe it easier in may cases to cultivate empathy for the unborn than to try to convince through logic or legalities. Religion is even more powerful, but of course not everybody is religious.
The proscription of behavior by law, with penalties attached to these proscriptions, does affect what people will chance, but more importantly, having something as heinous as abortion 'legal' lends the notion of 'okay', an acceptable alternative to taking responsibility for behaviors.
I was responding to your discussion of legal protection.You wrote
Then we get to the difficult issue of legal protection. I agree a human should not be killed, but I can't agree to any punishment for the perpetrator. The perpetrator could not possibly realize that a microscopic object with no human form and no ability to sense anything or communicate in any way is human. Protecting humans must ultimately appeal to our ability to empathize with them, not an abstract legal status. Unless you can demonstrate how we can empathize with such a human, I don't think protection is realistic.
It's not as though each mother-to-be (or mother-not-to-be) gets to write a law about each child she bears.
Society at large does that. And not everybody likes everybody else or likes everybody's offspring...[of course, it would be a nicer world if they did.]