As Ezra over at TAPPED and Kevin Drum have noted, many folks are discussing an article by Brink Lindsey at TNR on whether a fusion is possible between Libertarians and Liberals, to create a sort of neo-progressivism. Not being a subscriber to TNR and having no desire to join, I haven't read the article itself. However, this is a pretty old debate, and the reasons why the twain will never meet should be clear to anyone who has thought about the issues seriously. As both Ezra and Kevin note, the easy part is agreeing on the socially liberal positions. Libertarians are basically "leave me alone" types who dislike government interference period, so naturally they value individual privacy and do not like government prohibitions on personal conduct, such as drug laws, even if movements to expand the private sphere are mostly issues championed by the Left.
But there is a very fundamental difference between libertarians and liberals (and especially progressives) once one veers into the economic area. Although both words have their root in the Latin word for free, "liberal" comes from "liberalis," which meant "suitable for a free man," and has always been a synonym for generous. Libertarianism, on the other hand, focuses on individual liberty. Not to put too fine a point on it, libertarianism is a glorified synonym for selfishness, and therein lies the unbridgeable difference.
This becomes apparent when one considers Lindsey's proposed points of fusion. All join hands in the name of social liberalism, but he expects liberals to give up such bedrock concerns as entitlements as a safety net and the progressive income tax. But the modern liberal vision (as opposed to Edmund Burke's liberalism) is founded on a notion that what is "suitable for free men (and women)" is a fundamental level of not only social but also economic equality and security. In short, a vision of the common good that acknowledges the interconnections between everyone and, indeed everything, to the point that, as we used to say, "until everyone is free, no one is truly free."
This, however, is anathema to the libertarian, who believes in maximizing the freedom of those who can best take advantage of it, that is, those with advantages and without scruples. And this is why libertarianism is fundamentally selfishness dressed up as ideology: the true libertarian does not see why any man's freedom should be curtailed for the benefit of society, let alone for the benefit of another. Social Security? Don't take 6.2% of my wages just because other people are too stupid or poor to save for their old age or can't find employers who voluntarily put something aside for them. Medicare? Don't circumscribe my choice of a doctor (or more likely, my choice to charge patients what I want) so old people have some minimal level of care. And above all, don't take a dime of my money to support anyone else, let alone support the governmental structure that makes possible the relentless pursuit and possession of great economic wealth; I'll give it in campaign contributions, preferably unrestricted, instead.
It is precisely the pursuit of material wealth and economic power at the expense of everyone else, and the glorification of those who succeed at this enterprise, raking in hundreds of millions of dollars a year, that have brought us to a level of income inequality unparalleled for almost 100 years, and a public infrastructure that is rotting away.
Amidst those who adhere to Lakoff's "strict father" and "nurturant parent" worldviews is another group whom someone dubbed "Islanders"--people who feel little connection to society as a whole or to other people who aren't exactly like them, and show little interest in contributing to their communities, people essentially without compassion. These are the libertarians, who cannot understand the web of connections that bind people together and bind each of us to the whole. Because they cannot see or understand these connections, they have no interest, fundamentally, in repairing the tattered fabric of our society, especially the frayed safety net, or doing anything about inequality. Instead, they advocate things like the "ownership" society, in which the most aggressive own everything they can get their hands on (with the help of friends in government, of course) and everyone else is on their own.
It is ironic that so many in the generation who benefitted most from the generous public investments of the New Deal, World War II and especially the post-war investment in education, highways, science and technology, health care and so much more should have grown up falling in love with Ayn Rand and thinking that they got where they are solely by their own efforts, with so little compassion for anyone who could not or did not do the same.
I'm not saying that the programs of the New Deal or the Post-war are perfect. They do need updating as well as repair. But a society in which people fundamentally do not care about other people (especially people different from themselves) or understand how the whole is greater than the sum of its parts is a very unstable as well as a very cruel and ugly place to live. Until Libertarians show some interest in addressing the plight of the 75% or so who are treading water or slipping behind, I seriously doubt that there is much common cause that real liberals can find with them.