Running through a great deal of the anti-abortion movement is an undercurrent of an anti-sex movement. How much of the fuss is completely about abortion, and how much is about the sexual freedom that abortion potentially allows? In the past, getting knocked up meant stopping having casual sex, giving up the wild life, and settling down with the guy and becoming "normal", "decent", "traditional" people. Abortion is a way out of that. What was the end of the wild life for our grandparents' generation can be just a delay for a medical procedure today.
I'm not saying everyone who holds anti-abortion views is necessarily anti-sex, but I would be willing to venture that if you scratch the most militant activists you'll find people who disapprove of pre-marital sex, contraception, and the swinging single life, and possibly quite a bit of chauvinistic attitudes about women and men and how they ought to act.
Abortion is a concrete example of medical science and technology taking what used to be up to God, chance, or nature and putting control back into human hands. Whether that's a good thing or a bad thing, it is a big thing, and some people will always be uncomfortable with that.