Should governments let people trade kidneys?

The Economist discusses this question:

But human kidneys are no ordinary commodity. Trading them is banned in most countries. So supply depends largely on the charity of individuals: some are willing to donate one of their healthy kidneys while they are still alive (at very little risk to their health); others agree to let their kidneys be used when they die. Unsurprisingly, with altruism the only incentive, not enough people offer.