It is abundantly clear why the president feels compelled to veto this legislation. It isn't based on science, regardless of what Tony Snow may say, and in his topsy-turvy world of spin, the president is putting "science before ideology." (It is sadly ironic that Mr. Snow, who suffers from colon cancer, probably could benefit from embryonic stem-cell research.) It comes from a perverse point of view that there is a branch of science, conveniently merged with political and fundamentalist religious elements, that takes precendence over the majority of scientific thought, backed up by provable research, that says that embryonic stem-cells hold a greater hope than the "science" Mr. Bush aligns himself with; the "science" that also believes that the universe is 6,000 years old and that Adam and Eve shared the Garden of Eden with dinosaurs. The ideology that Mr. Snow is attacking is that science -- provable, factual, and possible -- takes precedence over a perverted sense of morality that elevates superstition and medieval alchemy above everything else.
What is even more maddening is that the president's motives are clear. He knows that his political support is based on the hard-core right-wing nutsery that believes that every sperm is sacred and that a Petri dish of embryos is entitled to the same protection under the law as a fully-formed human being. In fact, they believe these test-tube zygotes are entitled to more protection than someone with Parkinson's disease, diabetes, or a severed spinal cord. What they're really saying is that an unborn life is worth more than someone whose life is near its end. Hey, you had your chance; now its this little speck's turn. Sorry about that.
This mindset from Mr. Bush and his little collection of religious fanatics is another manifestation of what Glenn Greenwald so brilliantly describes in his book A Tragic Legacy (excerpt here).
One of the principal dangers of vesting power in a leader who is convinced of his own righteousness -- who believes that, by virtue of his ascension to political power, he has been called to a crusade against Evil -- is that the moral imperative driving the mission will justify any and all means used to achieve it. Those who have become convinced that they are waging an epic and all-consuming existential war against Evil cannot, by the very premises of their belief system, accept any limitations -- moral, pragmatic, or otherwise -- on the methods adopted to triumph in this battle.Mr. Bush sees embryonic stem-cell research, if not as an Evil, then as a slippery slope to Evil. Pure science, he believes, does not have an ethical contingent; all they seek are facts. Therefore he is the person chosen to stop it, and whatever the consequences of his actions -- whether more people suffer from illnesses, whether they spend the rest of their lives in wheelchairs -- is irrelevant to the goal of preventing the spread of Evil. And anyone who benefits from such immoral practices such as extracting stem-cells from embryos that were destined for destruction anyway are, by his definition, collaborators in the Evil and are therefore just as Evil themselves and do not deserve the benefits of a cure or treatment. They have been judged by the president and found wanting.
Efforts to impose limits on waging war against Evil will themselves be seen as impediments to Good, if not as an attempt to aid and abet Evil. In a Manichean worldview, there is no imperative that can compete with the mission of defeating Evil. The primacy of that mandate is unchallengeable. Hence, there are no valid reasons for declaring off-limits any weapons that can be deployed in service of the war against Evil.
Equally operative in the Manichean worldview is the principle that those who are warriors for a universal Good cannot recognize that the particular means they employ in service of their mission may be immoral or even misguided. The very fact that the instruments they embrace are employed in service of their Manichean mission renders any such objections incoherent. How can an act undertaken in order to strengthen the side of Good, and to weaken the forces of Evil, ever be anything other than Good in itself? Thus, any act undertaken by a warrior of Good in service of the war against Evil is inherently moral for that reason alone.
Forty years ago my grandmother died from what was then called "hardening of the arteries." She showed all the symptoms of what we nowadays know is Alzheimer's disease, but we'll never really know. As her descendant, it occurs to me that the same fate could await me or my siblings -- such diseases tend to run in families -- and I'd like to know that sometime in the next thirty years or so, there will be hope that science can overcome not just the mysteries of the chemistry that cause such a dreaded fate, but also overcome the ignorance and idolatry that hinders it. If that makes me Evil in the eyes of the president, then I will have to live with that. But at least I will be living.

