I think it's interesting that National Review's top online column at the moment is about how the real reason public-sector unions need to be busted is not because of the effect they have on states' bottom lines, but because they're quite effective at political organizing—whether or not they have collective bargaining rights. And this is bad for the public because ... well, mostly because those unions oppose GOP policy prescriptions.
I think it's worth noting that conservatives tried to temper criticism of of the Citizens United ruling by pointing out that unions would also be able to pour lots of money into campaign races—that it wouldn't just be the U.S. Chamber of Commerce and wealthy plutocrats. But there's a number of legislative efforts underway (and not just in Wisconsin) to dilute the power of unions to organize workers, pool their money, and actually offer substantive opposition to the plutocrats. If the GOP wins its union-busting fights, that will only compound the ability of the Kochs and Americans for Prosperity to flood races with money. Williamson argues that the amount of money and organization unions can muster somehow distort democracy—but he doesn't bother considering how that's also true when the money supports conservative causes.