As most of you will probably know, I have very little respect or appreciation for "moral" arguments. Although, I think there is perhaps one (which as a massive consequentialist streak) that you could make in favour of libertarianism. I'm not talking totally laissez-faire Ron Paul libertarianism, either. Just civil libertarianism and sensible policies which won't impede economic growth.
A lot of the time, people often ask why economic growth and efficiency is so important; why should it matter more than something else? And it's a difficult question to answer, although it seems - without being able to articulate it - that you're always going to want strong economic growth.
Well, it'd seem that all we need do is agree that politics is about making the most conducive decisions to human happiness and development. So, what does this have to do with an individualist, liberal society?
Elliot Turiel and Lawrence Kohlberg's - two of the earliest students of moral psychology - both posited that the nativist approach and the empirical approach were wrong. They suggested a rationalist explanation, that children will innately develop a sense of moral behaviour. Richard Shweder, however, came along with some evidence and threw it all up in the air.
A study conducted in Orissa, India, by Shweder, showed that Indians were more moralising (they stated that actions which simply violated social conventions were actually immoral; universally wrong). The main reason for this, Shweder said, was that India had a much more sociocentric culture.
Jonathan Haidt came along a few years later and conducted a similar study within both America and Brazil. He found, in both countries, that the less educated and more destitute had a higher propensity to be sociocentric and thus moralise more (like claiming that cutting up the American flag is universally wrong). Whereas the more educated and more prosperous people were more individualist, and permissive of actions which violated social convention, but didn't harm anyone.
Sociocentrism, as a means of organising society, has a very ugly history ranging from Nazi Germany to Soviet Russia. It is a very tribalist and intolerant means of organisation and, while maintaining higher internal cohesion, can lead to fractures and crimes against humanity on a considerable level.
It seems prudent, therefore, to offer a system whereby individuals are respected, economic prosperity is considered essential and liberty is guaranteed, while responsibility is enforced.
/ramble
The best moral argument for libertarianism