Egnor v. Rosenau on abortion

Michael Egnor continues his attempts to reason with ScienceBlogs writers. This time with Josh Rosenau, who provides a variety of poor, unscientific arguments for abortion.

This is especially unmoving from Rosenau:

We know, intuitively, that there must be a distinction between an egg cell gone wild and a baby. That it's hard to come up with a clean, uncomplicated distinction shouldn't persuade us that there's no distinction at all. But it should give us pause whenever someone claims that it's easy to draw a line between human life and everything else. And if that line is hard to draw, we may have to accept that fertilized eggs and embryos and fetuses fall on that border, and that there are a range of plausible ways to handle the cases on the border, and that this is a choice best left to individuals.

For one, the line isn't that hard to draw (is the entity an organism and if yes, is the organism human?), Rosenau just prefers the law discriminate against tiny, less developed human beings.

Second, why do only fetuses and embryos fall on the border? Why not infants? Rosenau provides no reasoning here. His same poor reasoning, (the line is difficult to draw, let women decide) could just as easily be used to defend infanticide and the killing of other dependent human beings. In reality, Rosenau is drawing his own line (at birth or late in pregnancy) but never provides any solid argument for why his line is clearer.

I'd also like to point out how important it is to provide and agree on definitions for words. In the arguments above, it's clear that Egnor and Rosenau are using different definitions of the word "discrete." Rosenau seems to be equating "discrete" with being "independent" which is clearly not what Egnor intended. Egnor appears to be using it to mean "distinct."