The primary issue I take with this is that the $40 payment to extremely poor Brazilian families doubles their average income, but in order to make an impact of that scale in the US it would take astronomically more. The success certainly makes it worth looking into though. And I agree with the idea on a basic level if done right. There is an unsettling separation of classes in the US. What's most interesting is the physical separation similar to the ones we often find ourselves creating in this country. There is a complete disconnect and distrust between entire population segments of the country and that never goes well for us. It certainly is the land of the free, but it's also indivisible. We're dividing it in favor of freedom, but only for a select few. I personally find it hard to reason that our recently developed tendencies towards winking and nodding at almost predatory profiting in the name of freedom are honest or just.
I don't know why I will bother with a response, since it's clear that according to the Atlas Forum consensus the solution entails members of the "owning class" redistributing their life savings away through confiscatory taxation to "poors" so they too can live like the owners (presumably before the confiscations took place) ... or whatnot ... but this issue is important to me so I will reply anyway.
I see two points in this post: Direct transfer payments can alleviate poverty amongst a rural peasant class, as it had in the American South during the 1940s, but I don't see that it has alleviated poverty in any way outside of it. Quite the opposite: the problems we see with the poor in the US stem as a consequence of the nature of the welfare that they receive -- the direct correlation between childhood and adult obesity and use of TANF and free/reduced school lunch program; high dropout rates from public schools that in any case cannot prepare graduates for even (rapidly diminishing) blue collar employment; high teen pregnancy rates, combined with high infant mortality rates, for single parents whose child and personal health care is provided free through Medicaid. These are systemic issues that cannot be ameliorated through yet another wealth transfer program, which already exists in the EITC, except to the extent that it allows the poor to escape the institutions of poverty like the food stamps, Medicaid, etc.
As far as your second point: Unless you have a means to prevent the free movement of the population, for whatever reason, your second concern is purely rhetorical.