Too many times people get up on the soapbox of the world and give their opinion about this or that policy, and one can never figure out whether they are experts speaking from experience or just political hacks.
They can also simply be citizens of this world, who might be impacted by such far-reaching changes to society, and who therefore justifiably want to have their say. I don't believe that's an unreasonable position. If someone wants to run an 8-lane road right next to my house I'm entitled to an opinion, even without a study backing me up. Similarly, if someone wants to change the entire system of incentives and capital allocation, to such an extent as presented here, I do believe I should be allowed to comment since it will impact my life as well.
People giving an opinion in public is just noise, and people bolstering their opinion with rationalization and/or analogy is noise masquerading as signal.
Public debate is actually the basis of democracy. If you want people to hold that debate in an informed manner, you should really provide them with sober facts, rather than opinion, handwaving, shouting, and threats. Just because presenting facts has gone out of style so spectacularly, is not at all an excuse to now also disqualify people from voicing their opinion.
I'm especially suspect of the "it will only encourage some people to work less" comment, as if that is a bad thing. It might be perfectly acceptable for some part of society to have to work less, or perhaps not to have to work at all.
This argument has two parts. The first is that nobody might be inclined to do any of the unpleasant jobs anymore. One could argue that society should simply pay more, then, but that assumes (as does UBI itself) that money grows on trees. The second part is the fear that we might find ourselves with too few people willing to work to keep society running _at all_. No police, no firemen, no teachers, no civil servants, no doctors - how would we end up? Some kind of Detroit where society slowly decays and gangs rule the streets? The assumption of UBI is always that people freed from financial concern will automatically proceed to either freely create value for others, or at least not bother anyone. That's a beautiful sentiment, but I'm not convinced it's automatically true.
As far as the facts go, the total cost of a nation-wide UBI program is the number of people times the amount each receives. This cost is invariably either much higher than the total cost (including overhead) of existing social security programs, or the amount received is far below what's needed to make a living.
An additional problem is that currently, social programs are tailored towards those who need it. Quite a few people simply don't need additional support, and any money given to them is unavailable to those who do need it. Are we supposed to think of this as 'fair'?
One might also wonder if money were created for free, whether cost (of everything) would remain the same, or rise to meet the levels of available money. In other words, the program might be undone by rampant inflation.
And I do believe it is a valid concern that politicians might very well attempt to subvert the system with all sorts of special benefits designed for their own constituents. It's what they do, after all - but as soon as you do this, the major benefit ("simplicity") goes down the drain.