um, yes it is.
you claim the bible says nothing about abortion, specifically. it says many things about the sacredness of life, about not killing, which can and does get interpreted in many ways.
There are plenty of "arms" with which one may arm themselves. Why would you ask for a direct, literal example from one source, as if it matters, then demand that it is unnecessary in another source? yes, we certainly feel that we have the proper interpretation, we certainly feel that we know what was behind the minds of the founding fathers, we can infer as much as we want to, and rather accurately, but that is all it ever is.
and that is why we have a SCOTUS--
whose only role is to interpret the constitution (this is why literalists like Scalia are fucking idiots--he doesn't even understand his job, lol)
Granted, I put much more stock in the Constitution than I do the Bible, as I believe you do as well--but the notion that it has to be word-for-word in the Bible is silly. Not that it was meant to be interpreted literally, anyway...but try and tell that to the pack of loons.