Don Boudreaux explains it quite nicely:
The “conservative/liberal” division – although thought of in America today as the two alternative, relevant “sides” of political opinion – is no such thing. If we talk seriously of two “sides,” a much more realistic division is between those persons with a fetish for centralized power and those persons who distrust such power.
Modern “liberals” long for Washington to design and control the economy in great detail. Modern conservatives look to government to engineer the polity’s moral tone... Despite their differences on particular policy issues, both modern “liberals” and conservatives have a fetish for centralized coercion.
So the side opposite both the modern “liberal” and conservative is occupied by those persons who are neither conservative nor “liberal” but, rather, deeply suspicious of entrusting government with power.
And these “power skeptics,” as we might call them, are far more willing than are “liberals” and conservatives to let individual men and women choose their own courses in life – to buy and sell and work as they wish; to save and invest – and ingest – as they choose; to partner with each other romantically, socially, and commercially in whatever peaceful ways they like and never in ways that they dislike; to keep the full fruits of their efforts and risk-taking, and not be coerced into subsidizing those who are less industrious or adventurous; and not to be forced to support military adventures that have no direct and compelling relationship to the protection of peace and property at home.
This is the nature of the political debate we should be having: Obama's agenda for a massive expansion of government, versus the platform that seems to be emerging from the Tea Parties. The Tea Parties are revealing a new political platform that has been obscured for decades by those who argue about whether the government should regulate such things as abortion, immigration, and marriage. Those debates were all about government intrusion in our lives. The new platform takes us back to our country's roots: less government, not more; less spending, not more; lower taxes, not higher; less coercion, not more; citizen politicians, not professionals. These are turbulent times, but, as Charles Krauthammer points out, they are also "politically and intellectually invigorating." Let the true battle begin. The stakes haven't been so high in generations.