But whether an embryo is sentient or if its life has more value than that of a dog or cow is a debatable point for people who don't derive their opinions from their dogma. If you take "pro-life" to be short for "pro- sentient life", then you've shifted focus away from the issue over to what's pretty much a tautology.

I agree with you that an embryo isn't sentient - however, they believe it is, or at least that it has a "soul" (which, in their minds, is the same thing). Their position is that wrong to kill something with a soul. You can (and should) be scientific about whether or not an embryo meets that qualification, but that's a question of their poor science, not their motive nor the position they think they're arguing...which I do think is reasonably accurately captured by "pro-life".