Perry de Haviland writes Libertarian Democrats? for Samizdata about the idea floated at the Daily Kos that one could be a libertarian on the left side of the American political aisle. The idea is that the corporation has to be counted with the government and the criminal as a threat to individual liberty. Perry points out that the problem with that is that corporate power only becomes corosive when coupled with governmental power. The Kelo immanent domain decision comes readily to mind.
In short, a corporation can only exert influence over and by what it owns. If you let the government have too much power, it becomes something worthwhile to buy. Check my last entry for a tongue in cheek take on that idea. But seriously, a corporation can only influence what it owns. People may have griped about Microsoft acting like a monopoly, but you certainly weren't looking over your shoulder for Bill Gates when you were last getting a physical. Nor would Wal-Mart have much to do with the cost of milk, what with the subsidies in effect. But in both cases, the government is right there, or threatens to be there. So why wouldn't corporations want to buy some of that?
Government influence is the ultimate contraband, and the only way to fight it is to cut off the production of it.