More plausibly, critics worry that super PACs encourage reckless mudslinging because candidates benefit from the groups' attacks on their rivals but do not have to take responsibility for them. When challenged about the accuracy of independent advertising supporting them, politicians can always say, as Romney did during Sunday's pre-primary debate, "that's something which is completely out of the control of candidates," who are legally barred from "coordinating" with super PACs.

But as Romney observed, "this strange situation" was produced by campaign finance regulations. Why not "let people make contributions they want to make to campaigns," he suggested, "and let campaigns then take responsibility for their own words"?

A good question. Critics of super PACs argue that they pose essentially the same risk of corruption as unlimited campaign contributions would, since politicians are apt to be grateful to people who help them win elections. Why not do away with the pretense?

Like prostitutes who masquerade as masseuses or head shop owners who insist their fancy water pipes are intended for use only with legal herbs, super PACs have a shady reputation because of misguided prohibitions. The limits imposed by the Federal Election Campaign Act gave rise to "issue ads," which provoked the ban on "electioneering communications" that was overturned in Citizens United; now super PACs are yet another means of getting around contribution caps.

"Improper influence" is a perennial hazard in politics. It can be kept in check by monitoring the favors that elected officials do for their supporters -- and, more important, by limiting their power to dispense favors. But it cannot be regulated away by increasingly creative restrictions on speech.