The Killer Argument is that if you replace means-tested and conditional welfare payments with an unconditional and non-means tested one, "people won't bother working".
That is clearly nonsense, assuming it is set at a sensible level - about £75 (with housing benefit and council tax reductions on top) a week, or something like £120+ a week if housing subsidies are scrapped. There are very few people happy to live off £6,000 a year, most people want and earn much more than that.
The conditionality (aka pointless persecution to keep the Daily Mailexpressgraph readers onside), might, in marginal cases push people into work. The means testing does precisely the opposite - there's not much point working for a low wage if you lose 75p for every gross £1 you are paid. And we know that the UK welfare system is so clunky and horrible that people on benefits are discouraged from taking a short term or insecure job because it's so difficult going back on benefits again when it ends.
The nay-sayers have of course had a field day with the results of a small-scale experiment in Finland:
Beginning in 2017, some 2,000 recipients of unemployment benefits were given a monthly stipend of €560, tax-free and without any conditions, as part of an experiment in simplifying welfare and lowering unemployment.
A preliminary report published on Friday by the Finnish welfare administration Kela shows that the experiment’s effect on unemployment or self-employment was almost nonexistent.
Which the BBC gleefully reports thusly: Giving jobless people in Finland a basic income for two years did not lead them to find work, researchers said.
Well, so what?
The real lesson here is that recipients were not discouraged from looking for work, which rebuts the actual Killer Argument.
So even if that is not an argument in favour of a Citizen's Income, it's certainly not an argument against it and the other findings certainly are in favour:
However [?], the recipients of the stipend reported feeling happier and less stressed than the control group, made up of those who received traditional unemployment and welfare benefits.
Which is a clear win, less expensive bureaucracy and faff and people are happier.
That 'happiness' would be much greater if everybody got it, rich, poor or middling alike. I'm not aware that rich people begrudge other people's free at point of use state education or NHS treatment, because most rich people use the NHS and send their kids to state schools, and even if they don't, they know they could. So it all adds to that vague but important concept, 'social cohesion'.