Philosopher Michael Sandel asked Greg Mankiw whether people should be allowed to sell their votes. Mankiw’s answer:

[T]he standard argument for unfettered voluntary exchange does not apply because there are externalities. That is, when one person sells his vote to another, that transaction may affect unrelated third parties through the electoral process.

On reflection, though, the sale of the vote is not the source of the externality. The externality comes from voting itself! This is precisely Bastiat’s argument for restricting the franchise to the well-informed:

Because it is not the voter alone who must bear the consequences of his vote; because each vote involves and affects the whole community; because the community clearly has the right to require some guarantee as to the acts on which its welfare and existence depend.

The lesson: If you’re afraid of vote-selling, you should be afraid of voting as well.