StampOutIgnorance -

I understand this seems to make sense to you, but your comment seems to very carefully skate around the central point.
An egg is "alive" only in the sense that it contains the potential for life. Same with sperm. 
But once the egg is fertilized, a fundamental transformation takes place. Your comment doesn't really concede this.
(Also, as to your point about birth: By this logic, it would be perfectly permissible to kill a 9-month-old infant when it is on one side of the birth canal, and yet not permissible to murder it five minutes later -- despite the fact that no measurable difference exists between the states, except for a few inches of distance. You can certainly hold this position if you want, but of course it would put you at odds with 99 percent of people, including even hard-core progressives.)