Atheists and abortion

It seems that pro-abortion atheists are used to dealing with pro-lifers who appeal to theology to support their position. I say this because when they encounter a pro-lifer who offers arguments demonstrating the humanity of the human embryo, they offer all sorts of non sequiturs, strawmen, and other baseless arguments.

My latest example of this is in my discussion of the humanity of the embryo with Ben, in the comments of this post.

Now, I've enjoyed my conversations with Ben thus far, and continue to do so. But neither he nor biologist PZ Myers have thus far offered a definition of a human being which excludes the embryo or fetus in a non-arbitrary and consistent manner. Nor, IMO, have they successfully refuted my arguments. But I'll let the readers of the comments judge who is more successful.