Dear Michael Sandel,
Thanks for noticing that I had started in the middle of things and for providing readers with an excellent statement of strict libertarianism. But to complete your statement, I should note that another strain of libertarianism has been developing over the last few decades among those who see themselves as part of the classical liberal tradition. Milton Friedman is a good example. He stubbornly continued to call himself a liberal into the 1960s, but even he had to give up eventually and begin to call himself a libertarian. I am of the Friedman school--which is to say, of the school that accepts the concept of public good and a slightly more permissive stance toward government action than a strict libertarian tolerates.
This is not the place to spell out those differences. (Quickly: Almost all of them involve government action with regard to education, the environment, and natural monopolies.) I raise the issue of public good to answer the question you posed: There is some daylight between me and the strict libertarians you described. But when I come to the three specific follow-up examples you posed, you didn't happen to catch any of the ways in which I depart. To wit: Yes, I agree with strict libertarians that licensing physicians is unjust. Social Security is wrong in principle. It is always wrong (again, in principle) to tax the rich to help the poor, assuming the rich haven't acquired their riches through force or fraud.
But to give these answers doesn't mean that I favor a society in which the sick are treated by quacks, indigent elderly starve, or the rich sip champagne while the poor huddle in cardboard boxes. Libertarianism involves two discourses, separate but not in conflict: liberty as a right, and liberty as the best way to organize society.
The discourse about liberty as a right--the one to which you alluded--uses a set of principles to erect a theoretical edifice that is internally consistent and all-embracing about what government may and may not do, independently of the kind of society that will result. The discourse about the best way to organize society draws from a tradition represented by Adam Smith in The Theory of Moral Sentiments, and one that remained robust throughout the 19th century: Given the mainsprings of human behavior, how is a just, compassionate, cooperative society to arise? My own preoccupations have involved related questions: How is it that people live satisfying lives (not just contented or amused ones)? What does it mean to "pursue happiness," and how do liberty and government fit into that pursuit?
The answers are complicated, and do not lend themselves to brief exchanges like this one. But they lead me to conclude that, while government wouldn't license physicians in a libertarian society, health for everyone, including the poor, would be as good or better than it is now. Life in a society without government-coerced Social Security would be richer and more satisfying on many dimensions than is life in the society we have now, including richer and more satisfying for the elderly. The size and misery of the underclass that is with us under the welfare state would be much smaller if taxing the rich to help the poor were constitutionally forbidden. Liberty is both a right and expedient.
Which brings me back to the libertarian proposition about community with which I began this "Dialogue": These days, community is a buzzword. Democrats and Republicans alike say all the right things about civil society. But if you really want communities performing essential functions, the practical, expedient way to get them is through authentic freedom. In a libertarian society, the surest way to make a life for yourself in an uncertain world is to be embedded in institutions involving family, faith, vocation, and community. This reality and the way this reality affects the socialization of each new generation systematically foster vibrant and active communities engaged in the stuff of life. Absent such a reality, such communities fade and eventually disappear.