Well, taxation is theft, so that is the easy answer to that. :-)
But to dig a little deeper... a UBI is an interesting concept, and especially so when one considers a future where most, or even all, human labor becomes unneeded. In a world of 100% technological unemployment, it does seem that we're going to require a different system than what we have now. But I don't think just saying "have an UBI" is much of an answer, because - IMO - the entire fundamental basis of the economy will be so radically different that we can't even imagine how the UBI will be funded and how the economy will work.
I keep running through scenarios, trying to come up with a scenario that makes sense, even hand-waving around the "initiation of force" issue temporarily, and it always seems to come out looking like a Ponzi scheme in the end.
Luckily, I think we're still quite a ways away from the total obviation of need for human labor, so we have some time to figure it out. Well, hopefully anyway.
Here's what you do:
1) Tax the monetary gains made by corporations from greater automation, not enough to disincentivize R&D, but enough to counteract inflation from step #2.
2) Institute an unconditional basic income, like Alaska already does for natural resources. Everyone gets a check in the mail.
You balance #1 and #2 so there is no net inflation. The more corporations lay people off in the aggregate, the more wages will be replaced by UBI.
I believe that an individual should be allowed to save the results of their work and consume the benefits later. I believe that they should be allowed to gift (or share) these savings with someone of their choosing. I don't believe that these allowances should be voided by death.
From that, I conclude that if my wife and I die with $2MM estate and give $1MM to each of our children, that they are entitled to the income from that capital, but it doesn't change the fact that that income originated from (my wife's and my) work.
And the problem with that is that it really relies on a "facts on the ground" view on property entitlements. If our laws about property are man-made and supported with force, why shouldn't we change how they can be transferred (or possibly voided in case of death?). You can disagree, and you certainly can fight it, but you can't really morally condemn anyone for trying to take it from you.
You can disagree, you can certainly fight it, but you can't really morally condemn me for sharing my earnings with my family.
But you're, as I said, not justifying it with desert now.
You think you deserve to be able to do as you wish with your money. But why do you deserve that? It can't be because you worked for it, because in giving money to people who didn't work for it (e.g. your kids), you acknowledge that having worked for it isn't important to you. And I guess you think that your kids, too, should be allowed to use the money you give them as they see fit.
Apparently, having the money ("facts on the ground") is sufficient for you to think you should be allowed to do with it as you please. That sounds like might makes right to me...
I'm not condemning you for "sharing your earnings with your family", but I'm certainly condemning your deficient justification for it.
If I have property rights over a steak or a measure of rice, I can cook it and share it with my family. Likewise with my house, car, or abstract medium of exchange (money). I don't see that as "might makes right", but rather as "that's inherently what property rights are".
But let's use your dictionary where property rights are always unconditional. In that case, we have never had property rights and it doesn't seem like a good idea to get them!
Libertarians do not say "people should keep their money because they worked hard for it." They say that "people should keep their money." No qualifier.
Libertarians are not "against force and for voluntarism." Libertarians are fully in favor of force, particularly when it comes to the defense of personal property. Some libertarians are in favor of voluntarYism (the y matters) but that's a totally different thing than whatever Bruenig trying to reference here.
It's partisan screed that oversimplifies concepts and twists words to appeal to people who don't actually know enough about libertarians to spot the bullshit.
There are three possible answers to that:
* Desert: It's mine because I deserve it, having worked hard for it.
* Contractualism/Voluntarism/VoluntarYism or whatever you want to call it, the idea that the arrangement is fair because it was all voluntary from the involved parties.
* Tradition: It's mine because however I got it, now I have it, and you can't take it from me. I call this the "facts on the ground" argument. It's not really a moral argument, so if you take this approach you can't morally condemn people who challenge the status quo (want to take it from you). If you leave out a justification for property claims, you're really here by default.
These three answers are not compatible, for reasons explained at length.
It's not bullshit, because it's a clear argument that I can follow. Whether it applies to "real" libertarians is another matter - as far as I can see it does, though.
I will refer the following article to show how tragedy of the commons did not happen in common land in the last couple of centuries:
http://www.thelandmagazine.org.uk/articles/short-history-enc...
* People should keep their money, they worked hard for it!
Then Bruenig points out that there is capital income, which does not come from work. Capital will keep "working" for you even if you stole it or inherited. It's extra obvious in the case of owning fully autonomous robots that could do anything a human could, but it's true for much simpler forms of capital, too.
Then they retreat to voluntarism:
* OK, so capital owners didn't work to get that money, but it was all voluntary. I'm just against force and for voluntarism.
Then he points out that property rights are enforced through violence too - the only reason you will make those "voluntary" trades for food and shelter, is that men with guns will come and arrest you if you just take it.
Then libertarians retreat to common-goodism:
* OK, we could imagine a society where people could just take as they please, so property rights are in a sense man-made. And they do require violence to enforce. But not having them would lead to the tragedy of the commons. Without property rights, we would all be miserably poor!
And this is certainly true, but if the common good is what we target, why not have a proper welfare state, a solid UBI funded by high taxes etc.?
Usually at that point they go back to the first step.