I think this stems from the fact that basic income is theoretically sound to anyone with even a rudimentary knowledge of economics. Now of course, it's DEFINITELY dangerous to assume that "theory supports it" is a slam-dunk case for anything, but preliminary results with pilot programs have also been encouraging[1] (the results have been fantastic, but the reliability of the data is not completely sound given how limited the programs are and how early it is).
Between the fact that theory supports basic income and preliminary pilot programs provide (on-balance) cause for cautious optimism, it seems that the burden of counter-proof is squarely on the side of those saying "Of course it could never work", particularly since I personally have never seen an HN comment providing anything to back that up beyond "It's just obvious, can't you see". I haven't seen any data OR plausible theoretical explanation provided as a counter to basic income.
Ah! A Link! Well after some review of the information on that Wikipedia article it is clear that all income pilot programs have only been administered to a minor degree in third world countries.
The ideas of administering this system on a LARGE SCALE in a 'well-developed' country such as the US would probably bring many of the problems Friedrich Hayek theorizes it would.
From Wikipedia:
"It is obvious that for a long time to come it will be wholly impossible to secure an adequate and uniform minimum standard for all human beings everywhere, or at least that the wealthier countries would not be content to secure for their citizens no higher standards than can be secured for all men. But to confine to the citizens of particular countries provisions for a minimum standard higher than that universally applied makes it a privilege and necessitates certain limitations on the free movement of men across frontiers... we must face the fact that we here encounter a limit to the universal application of those liberal principles of policy which the existing facts of the present world make unavoidable."
In other words people would flock from all over the world in DROVES to secure a spot in the unconditional free money system.
As with most economic policies, the degree to which it is implemented correctly is not linearly related to the quality of its outcomes: often one hole in correct implementation can torpedo the entire thing. In this case, providing a basic income is incompatible with open-borders immigration policy (i.e., limiting immigration to those who are likely to create more wealth than the cost of a basic income).
On top of that, this is almost irrelevant to the discussion of basic income. This is not a problem with basic income, but simply "differences in expected income across countries". The higher expected income that the US produces ALREADY has the effect of drawing immigrants from poorer countries here, and we already have a system in place to prevent this from happening (too) en masse. This has been happening for over a century. I don't see why providing a basic income would appreciably increase this effect, or why the "flocking in droves" issue would suddenly become insurmountable when we've already been dealing with the same issue (without ruining the economy) for decades.
Note that I'm discussing economic soundness here. It's totally possible that the vagaries of the American political system may prevent a key part of any economic concept from being implemented correctly, in which case all bets are off, of course.
Between the fact that theory supports basic income and preliminary pilot programs provide (on-balance) cause for cautious optimism, it seems that the burden of counter-proof is squarely on the side of those saying "Of course it could never work", particularly since I personally have never seen an HN comment providing anything to back that up beyond "It's just obvious, can't you see". I haven't seen any data OR plausible theoretical explanation provided as a counter to basic income.
[1] http://en.wikipedia.org/wiki/Basic_income#Examples_of_implem...