Great question. At the core it's a matter of "principle" over "practicality" or
Deontological libertarianism vs.
Consequentialist libertarianism. The former reject the State based on grounds of morality, that it is wrong to use coercive force on anyone, the State relies upon a monopoly of coercive force, so the State is immoral; the latter focus on the practical benefits of small government, the efficiency of the markets and how a free society is the most prosperous society. There are many "anarchist-libertarians (or
anarco-capitalists)" in the Deontological ranks, not so many in the Consequentialists.
There is also a large issue in terms of economic philosophy.
The arc-Deontological libertarian is
Murray Rothbard who is the major disciple of
Ludwig von Mises. Mises and Rothbard are seen as the pillars of
Austrian Economics (Mises came from Austria and continued a liberal economic tradition that really originated in Vienna with
Carl Menger and
Eugen von Böhm-Bawerk.
Austrian Economics, not unlike Milton Friedman, advocate free markets (no regulation, free trade, no prohibition, etc.) the biggest difference comes in the form of banking. Austrians vehemently oppose Central Banking and view it as the cause of inflation and market crisis.
Austrians were among the ones that quickly identified, and warned about, the housing bubble.
The real "base" for these libertarians is
the Mises Institute.
Meanwhile the leader of the Consequentialist libertarians is really
Milton Friedman. Milton Friedman's coined his own economic philosophy,
monetarism and his work is often referred to as "the Chicago School" (he was a long time Professor at the University of Chicago). Friedman was actually initially a
Keynesian economist, an economic philosophy that views a role for the State in handling and reducing the effects of market recession, and developed his belief that such state intervention should not come from fiscal stimulus, as Keynes advocated, but through monetary policy. Friedman believed that by increasing the availability of money, you can jump start the economy and get it running smoothly again.
This is what Greenspan did following the dot-com burst and 9/11. He lowered interest rates, which boosted the housing sector, which generated a lot of jobs and made a lot of people rich. Unfortunately when you print money you don't actually create wealth, so when the money finally made its way through the system, housing prices dropped and the bubble collapsed.
But I digress.
One of the most famous Austrian economists is
F.A. Hayek who won the Noble Prize in 1974. Hayek is unique because he kinda straddles the fense. He was a student of Mises, but ended up teaching, along side Friedman, at Chicago. Ayn Rand, who loved Mises, hated Hayek because Hayek always based his defense of the markets through social utility rather than on it's own moral merits.
Now there is a whole interesting history involving how the two different camps split apart,
the Koch Brothers even play a starring role, but that's probably more than you wanted to know anyway.
Why? I mean 1., the GOP establishment wouldn't have any say on Paul's decision, but 2. Rand Paul is a US Senator and the closest politician in Washington to Ron Paul's beliefs. It's not as if they were attaching some unqualified hack on the ticket because daddy want's him there, the reality is that there are few choices better to serve as a potential replacement to Ron Paul.
I think a libertarian voice has the best chance in 2012 than we have had in a long, long time. But Ron Paul's voice is stronger.