The truth is that a law banning the killing of unborn babies, just like a law banning the killing of 2-year-olds or 92-year-olds, is not based on denominational religion. It is based, rather, on applying an objective moral principle to an objective fact in the interest of protecting a basic human right. The moral principle: It is wrong to deliberately take an innocent human life. The fact: The unborn child (as Kerry himself "believes") is a human life, just as the 2-year-old or 92-year-old is a human life. The basic human right preserved is the right to life itself.
Yes, the objective moral principle here comes from God -- as does "Thou shalt not steal," which protects the basic right of private property -- but it does not belong to any religious denomination. It is universal and precedes them all. It applied when Cain killed Abel; it applies when each American president puts his hand on the Bible and takes the oath of office.
Presidents may pursue policies that accord with this principle or violate it. They can act rightly or wrongly. But they cannot change the principle itself -- any more than they can change the facts of human biology.
Kerry's argument that he cannot apply his own "belief" on when human life begins to how he acts as a lawmaker is not only absurd, it explodes his claim to leadership. If he won't act on his own "belief" when he believes human lives are at stake, when will he do so?