". . . I think most people who think about it believe there's no relevant difference between those little creatures."

Then why has infanticide never had any serious traction? They are regarded as "different" because the fetus is still attached to its mother. Logic would dictate that if they are the same and a woman is undergoing a late abortion, she may as well deliver and relinquish. And yet late-term abortion candidates don't do this. Why? I can think of lots of reasons and certain ones are straightforward and logical and others are not. 

"Finally, I agree that "I should think . . . more about why women get abortions in order to figure out how to save human lives." . . . But this doesn't mean abandoning an appeal to reason."

My point is, maybe it does. Human motivation is not logical. In order to understand, you need to get inside her head. This is something the pro life movement never does.