From another forum, this post, which I believe says it all:

"Interesting that there is a debate about killing beings in utero (one at a time), about which there is also a debate as to whether they are viable or not.

There doesn't seem to be a debate about killing actualized, cognizant, viable human beings in wars, bombing hundreds or thousands to death at once. Interesting.

I wonder if it could have anything to do with the fact that one act is performed by women, and the other by men....