As far as Christianity goes, equating Abortion to murder has only recently become the popular interpretation. Not only is it written multiple times in The Bible that life begins at breath, The Bible even contains instructions on how and when to perform abortion.

As far as the constitution goes, amendments are treated as part of the text, not gotchas. The constitution protects your right to keep the contents of your pockets and your home private. Why not the contents of your uterus?