“What’s with all the teenagers without costumes coming to my front door and expecting candy?!” This was the gist of several Facebook status updates I saw last night. I don’t discriminate against the uncostumed because it isn’t worth ruining someone’s evening to save a dollar or so worth of candy, but at least one friend has a “no costume, no candy” policy that’s not always popular. Halloween is an interesting object lesson in the law of unintended consequences: when we say “hey, come get free candy,” we can expect (predictably) that a lot of people are going to invest in getting that “free” candy. People will be disappointed to see adults and teenagers without costumes “taking advantage” of their neighbors’ generosity and then either attach strings or complain about Them, the people coming from outside Our Neighborhood to get the candy that we bought for Our Neighbors. It’s probably good for at least a couple of days’ worth of neighborhood gossip and/or venting on social networking sites. Social capital erodes (and prejudices might be reinforced) as we come to see people from outside Our Neighborhood as cynical opportunists. And so on.

So the policy question is this: if giving away candy bars at Halloween is going to be so divisive and problematic, why do we expect large-scale tax-and-transfer programs involving billions of dollars to succeed harmoniously and without cynical opportunism?