It was stem-cell research that finally got him not to sign a bill. Again, I am somewhat sympathetic to Bush's position on stem-cell research. While I am not certain, by any means, that a fertilized egg is a human being and I know that there are all sorts of problems with notions of potentiality, I also know that in a fertilized egg we have the material (in some sense) to make a human being, at the very least the genetic code that will be instantiated in the completed person. Bush thinks that killing fertilized eggs (byproducts of the process of in vitro fertilization in which more eggs are fertilized than can be used) in order to do research on the stem cells crosses a moral line from which there is no return.
One important issue here, though, is what the alternative is. Although there are some instances, witnessed by the children from adopted extra fertilized eggs present at today's veto, in which these fertilized eggs are implanted and become children, the vast majority of such eggs will ultimately be discarded.
So, it is largely not a choice between using these eggs for research and treating them with dignity. It is a choice between using them for research and discarding them. If there is a moral line being crossed, the line is crossed when we fertilize eggs in the labs of fertility clinics and then do not implant them. Once we have them sitting around in freezers, we are no longer in the moral position to talk about what treats them with dignity; unless we are willing to demand that all of them get a chance at life. Instead, we really are in the realm of deciding how we can treat them in ways that best serve the rest of the population; the issue of their dignity has passed. Perhaps the answer is to rethink our policies with regard to fertility. Why is it that we think that everyone has a right to a child of their own, or that infertility is a problem to be solved? And, if we agree that this is a right or a problem that our doctors should solve, then why aren't we troubled by the creation of extra fertilized ova?