I don't feel that embryos are "persons" at all, in fact the only reasons I've seen to be against stem-cell research are religious ones. I admit, I haven't comprehensively studied the issue, but from what I have read, that seems to be the case.
I decided that my response was worthy of a post, which I've cross-posted at Philosophy et cetera. You don't need to know much of the abortion literature to know that this is wrong. All you need to do is pick up any of a number of standard applied ethics anthologies to know the most common argument for embryonic personhood. Most of them contain John Noonan's paper defending the traditional pro-life view, and that is indeed a philosophical argument, no matter how bad you might think the argument is.
The first premise is that a newborn is a person and has full moral status. The second premise is that personhood or the kind of moral status persons have is not the sort of thing that can admit of vagueness. But then there's no good place to draw a line between embryos and newborns that is not vague, and thus embryos must have the same moral status as newborns. You may disagree with the argument, and there are all sorts of ways to do so (but none that I know of that aren't question-begging). Even so, I don't know how anyone can deny that it's a philosophical argument.
I know lots of pro-life people who aren't exactly the philosophical type, and pretty much all of them will put forth something like this when questioned about why they think an embryo has full human rights, though they will do it without the philosophical sophistication of John Noonan's version. If anyone is going to stick with quoting scripture, it would be these people, and yet they're well aware of the philosophical argument that stands behind most versions of the pro-life view. I don't see anything in the argument that quotes scripture or gives a dictate from a religious authority of any other sort. For a more detailed presentation of my own view on what I think the arguments on both sides can establish (or at least what I thought two years ago, since I may have changed a little on some points), you can see this post.
I don't mean to suggest that religion can't provide anything that might help flesh out a pro-life view. I think the opposite is true, actually. I think religion can provide an account of exactly what the difference between humans and other animals are, a difference that gives humans what might be called deontological rights and animals what utilitarians might call rights (i.e. trumpable or rule-of-thumb rights). I explore that here, but I don't think my account of that is by any means the dominant one. It's just the one that makes the most sense to me consistent with what I do think reason can tell us and what I think the Christian scriptures teach. But I don't consider this to be an argument for the pro-life view, just an account of how to make sense of one of its views.