Should the state provide a baseline income to all adult citizens? It need not be a lot - though it could be - but even a few thousand dollars a year would surely help many of the less fortunate in our society. I think it is a much better idea than targeted (non-universal) welfare benefits, for several reasons.
1) It avoids the "poverty trap" of perverse incentives, since the UBI is not contingent on staying in a bad situation. If you find a job, that's all extra money on top of the UBI. You don't need to worry about losing your benefits if you become successful.
2) Since everyone receives it, there is no stigma attached.
3) Since everyone receives it, it may generate less resentment. Nobody gets "special treatment". People might be more willing to support it since they too are among those who benefit. (Though that may be somewhat deceptive -- the rich will be paying more extra in tax than they will receive back through the UBI. Still, for middle-income families it would probably work out more evenly, and they might well appreciate the security it offers.)
[Updated to add two more reasons:]
4) Any "targeting" criteria will be imperfect, depriving some people who are in genuine need, and benefiting others who are not. This is because any criteria will rest upon sociological assumptions about, e.g., indicators of need and merit. These assumptions are "naturally prone to sociological error and to social change", as Goodin points out. The UBI, by contrast, is a "minimally presumptuous strategy" - it relies on fewer sociological assumptions, and so is less likely to go wrong.
5) The UBI could, potentially, benefit the economy. The linked post also points out that the UBI would increase the bargaining power of the worst off, thus protecting them from exploitation, and relieving the need for many market regulations (e.g. minimum wage laws).
On the other hand, two main objections spring to mind:
(i) "Why pay welfare to the rich? They don't need it!"
This is a poor objection. As already noted, the rich will actually be paying more into the scheme than they get out of it, so it's not as if we're doing anything so absurd as redistributing wealth to the rich. As for more positive reasons, see the three already mentioned above.
(ii) "Why pay those who contribute nothing to society? They don't deserve it!"
This is by far the more pressing objection (to all forms of welfare). But how many people does this really apply to? Surely the vast majority of citizens work in jobs or their community, or care for children. (Note that a valuable social contribution need not be economic.) Only the most spectacularly dismal life would truly contribute nothing, in this broader sense, to society. Even if there were a few such bludgers, we must recall that the law is a blunt instrument, so will never yield a perfect result. So long as the policy does more good than harm, it's worth supporting nonetheless.
Besides, it isn't obvious that anybody has grounds to complain of unfairness. If you really envy the surfer or the bum who bludge off the system, then you may join them. Quit your job and sit around watching T.V. all day (assuming the UBI is enough to live off, which it need not be in any case). Not so tempted after all? The fact is, most of us want to work. (Perhaps not so much as we currently do -- but then, I'm all in favour of people working less and reclaiming their time, and a UBI would help enable more people to do this.)
Finally, we might try to modify the UBI so that it wasn't fully "universal" after all, but rather, was only given to those who made a sufficient contribution (in the broad sense) to society. This would be harder to administer, but it might become necessary if there were too many free-loaders. And it would put to rest the "fairness" objection.
What do people think?