It's important to emphasize that right now, the responsible thing is to perform extensive experiments on how UBI will affect work incentives. There are lots of unknowns, and this will give us some information to formulate later questions, once results are actually reported.
Not necessarily: if the purpose of the test is to determine how basic income affects outcomes over a period for the unemployed, having the experimental group to whom BI is given be exclusively drawn from the set of people unemployed at the beginning of the experiment and comparing that to a similar group of unemployed people not given BI is a fairly sane experimental design.