Actually, if you look into the Terry Schiavo case, you'll find that a lot of her brain was still intact, including portions responsible for personality and memory. The brain isn't a homogeneous structure, but a series of complicated parts layered over each other. While it looks like about 70-80% of her brain was liquefied, any (currently nonexistent) treatment that somehow restored the damaged regions and allowed her to start functioning again would have unknown implications for her personality. Certainly, there'd be changes. But "best you've done is manufactured a new person from spare parts" is both speculative and hyperbolic.
But you've completely missed my point in the first place. The "sanctity of life" isn't based in one simple philosophy that can be dismissed as mythological simply because "pro-lifers" are inconvenient to your enlightened preferences. There are folks who think a living, human embryo is a living human being. There are folks that think a brain-dead patient is a tragedy, but still a living human being. There are people who accept that an embryo lacks psychological characteristics of a fully developed human, but still see late-term abortions as murder. And there's a whole continuum of other ideas tangled up this issue. While you've clearly positioned yourself as philosophically superior to each of these individual camps, you're going to find that if you dismiss each group that doesn't agree with you, you'll quickly whittle yourself into such a minority that you'll have no political support for your refined wisdom.
And that's what's at work here: politics. You don't get to choose for the rest of us what's right and wrong. We all do, together, and you get to suck it up and go along with us. You're welcomed to rant and rave about superstitions and brain-dead patients all you want, but, like I said, as long as you chase off everyone else who supports you, you're not going to get anything done but make lone posts on a discussion board somewhere with all the effectiveness of a self-ostracized malcontent. "But without falling back on spirituality..." -- is the core of your problem on this issue: politically, you don't get to disenfranchise the religious of their spirituality just because they honestly and fervently believe that killing human embryos is against the wishes of some gray-whiskered old fart in the sky. They are going to write letters, vote for representatives, and get legislation that enforces their beliefs. Because of 1st amendment guarantees, everyone gets to do that, regardless of what you or anyone else thinks of their reasoning.
Person-to-person, just between you and me? I'd hate to see those embryos wasted, and this seems like a perfect use of them given that they aren't likely to ever get the chance to develop into cooing, giggling, drooling little babies anyway. But I'd also have reservations against instituting any sort of assembly-line process that funds the production of embryos solely for their use in scientific research or pharmaceutical production. That's moving in to Soylent Green territory, and most people think that's creepy.
