But I would not equate it with hiring one. That's because the expected damage from planning to hire a hitman is smaller than that from actually hiring one. A year of punishment hurts the criminal the same regardless of which of those two scenarios holds, but the social benefit of punishing them is less. Therefore we should punish them less. (Unless we don't care about the welfare of someone who's been convicted at all. I think that's a sick position to hold -- even setting aside the possibility of false positives -- but it has its adherents.)

A real eye-opener for me regarding these questions of weighing the costs and benefits (i.e. the economics) of punishment was Thomas Friedman's book Law's Order. Until I read that, I thought the whole question was just a political fight. And while it certainly is a political fight, there's a much more objective kind of analysis available -- in fact, it's the norm in economics.