Let's assume for the sake of argument that the US Congress actually passed a UBI bill that was simple, elegant, and did not have a bunch of complicated amendments tacked onto it. Let's say they passed a bill stipulating that every person in the United States would get a check from the government every month, and that every check would be for the same amount. Let's also assume that the bill replaces every other welfare program with UBI, like the libertarian proponents of UBI hope will happen.

Even if that happened (and it certainly would not), it would only be a matter of time before it gets messed up. There are a lot of reasons the current system is the way it is. There are many reasons the voters would want some people to get more money than others under UBI, and many of them would be convincing. For example, should single mothers get more UBI money? What about cutting benefits for convicted felons? What about more UBI money for people in high-cost-of-living cities like New York and San Francisco? What about more UBI money as a form of affirmative action for certain racial groups? People will vote for some of those changes.

We would therefore end up re-creating a lot of our current welfare programs within UBI, for the same reasons we created those programs in the first place. Tyler Cowen has written more persuasively on this topic here: http://marginalrevolution.com/marginalrevolution/2013/11/wha...

UBI proponents have a few questions to answer: how can we afford it, how will it work, and how can they prevent it from being turned back into our current welfare programs under a different name? And how can they prevent the voters from simply voting to give themselves more money, thereby bankrupting the government?