Here, for the blogospheric record, is why:
1. I'm a libertarian. I agree completely with Thomas Jefferson that the greatest threats to our freedom and well being come from government, democratically elected or not. Certainly Hitler and Stalin tragically proved that. I think the Constitution in general, and the Bill of Rights in particular, must be strictly adhered to. Of course, not all the Amendments are exactly the same in what their wording prohibits. The First Amendment's provision that "Congress shall make no law" abridging freedom of speech and press means just that - "no law," period - in contrast to the Second Amendment's provision that the right to bear arms "shall not be infringed," which I take as meaning laws regulating weapons are constitutional, as long as they do not "infringe" on lawful citizens who bear arms. The Fourteenth Amendment, and its provision that all limitations on the Federal government in the Constitution apply to the states, municipalities, etc., is also crucial.
So are other components of the Constitution. I believe it is ethically horrendous to send people to war without the Declaration of War required by the Constitution. The United States has gone to war that way in every war we have fought since World War II.
I also think that, in general, the government should keep its hands off commerce and business.* I disagreed with the anti-monopoly suits against Microsoft - why punish the organization most responsible for bring us the Web?
I want to see lower taxes for everyone, except millionaires and billionaires, whose taxes should be raised. Indeed, I'd recommend no income taxes at all for anyone or compay earning under a million dollars a year.
2. I'm a progressive. This means that I think some government activities are not only necessary but ethically mandated. I want the government to do all in its power to eradicate social injustice, and insure equal rights for women (including a woman's right to decide whether or not to become a mother), gays (including the right to marry), and all minorities and majorities. The government should also make sure that people have sufficient health care, and do not live in poverty. I also want the government to do what it can to support and stimulate science, research, and space exploration. Federal spending should be directed to all of these social, economic, and scientific imperatives.
Neither the Democratic nor the Republican Party has been too good on the libertarian issues in the 20th century. Neither is Barack Obama or John McCain.
But Obama is far more progressive than McCain. I voted for Obama in the New York primary, and will vote for him in November.
*Note added January 2, 2009: And what do I think is the best response of the government to the economic crisis that struck the United States in the Fall of 2008, and is getting worse at the beginning of 2009? Here is what I wrote in a comment, below, on December 29, 2008: "I see the government as an antibiotic: we're usually better off, when fighting infection, to let our body's immune system do the job. But if our lungs are filling with fluid from bacterial pneumonia, we'd better be taking antibiotics (=government intervention in the economy) soon." And I would emphasize that the antibiotic intervention should be as massive as possible, and the government should be ready to try a new course of antibiotics, as rapidly as possible, if the courses being administered do not work. And just as with any strong medication, once it has done its job, it should be withdrawn, in a careful, measured way, as soon as possible.
**Note added December 3, 2011: See also A Progressive Libertarian in the Occupy Wall Street Age
13-minute podcast on this subject, which I recorded on January 2, 2009