CNN informs me that Rick Santorum just won Alabama and Mississippi — albeit the count shows Romney and Gingrich not very far behind. Whatever. It's time to look at the politics of abortion, contraception, and (not yet mentioned in this campaign) masturbation.
For all human groups, throughout history, survival has depended on numbers. When two tribes had to work out who got the river valley and who got the desert, the big tribe got the prime real estate and the small tribe got to wander in the wilderness. It's no different with religions. The more adherents to a faith, the more likely it is to survive. "Be fruitful and multiply," sayeth the Lord. If you don't, those damnable Egyptians or Hittites or whatever will wipe you out.
Increasing your group's numbers depends on keeping your women pregnant. Naturally, it follows that religions competing with other religions for population will have "moral" prohibitions against birth control, abortion, and that "sin of Onan," which "wastes" what could be used to keep the group's women perpetually pregnant (and don't forget to kill the queers.)
In the United States, "mainstream" Protestants, secularized Jews and Catholics, and those with no particular interest in any religion are failing to be fruitful and multiply, perhaps under the impression that they can do more for one or two children than for seven or eight — while traditional Catholics and Muslims, Mormons, and many Evangelicals are breeding like bunnies.
In a democracy, the breeders, eventually, will win.