2: Entitlement. A lot of people will decide that they are entitled to that money, that it is not enough for whatever arbitrary minimum lifestyle they decide they are entitled to, and that the police power of the state should/will/must be used to confiscate the difference from taxpayers.
In fairness, all should contribute to society at least as much value as they derive from society (at least insofar as they are physically & mentally capable). Giving people enough to live on while requiring nothing of them screws up the human psychology of self-worth: they can exert $X of effort/skill and get $X, or do nothing at all and get $X ... meaning their effort/skill is worth nothing.