> you don't want to increase the UBI amount because it'll cost you more than it gets you

I think this is an oversimplification, because in practice, there will be a gradient of people around the inflection point who would be willing to take less in order to stop working, and that gradient will vary by the individual and by the job.

Additionally, I can also imagine politicians promising increases to the UBI without concomitant tax increases, funded by bonds or other kind of financial mechanisms for monetary injection whose long-term negative externalities would be easy to obfuscate from voters.

> Imagine a world with widespread automation and general or close-to-general AI without a UBI.

This is the key point. UBI is (in my current opinion) a necessary tool for smoothing an economic transition to a highly-automated level. However, I am concerned that it might induce other economic instabilities such as in tax rates, voluntary or involuntary unemployment, underemployment, inflation, borrowing, minimum wage, and so on -- these instabilities could then spread to social or political disruption that would undermine progress towards the transition that UBI was originally meant to support.

Since the size of the UBI would roughly correlate with the size of its influence economically/socially/politically, then as the UBI increases, the variance of these potential instabilities would also increase. As such, increases to the UBI should be carefully controlled, for example by gating them to developmental milestones. Of course, that opens a whole can of worms on who sets the milestones and so on, so I suppose it's really just shrugging and hand-wringing all the way down.

> I think this is an oversimplification, because in practice, there will be a gradient of people around the inflection point who would be willing to take less in order to stop working, and that gradient will vary by the individual and by the job.

This is less of a problem than you would think, because the people for whom this is the case are the exact people who would already be in the "make it higher" camp.

Suppose you make $20,000/year from your job ($15,000 after tax) and then get a $12,000 UBI, so $27,000 in total. $12,000 is less than $27,000, but maybe if it was $15,000 and then you didn't have to work, you might be willing to take the pay cut. But this is the same person who benefits from raising it to $15,000 even if they continue to work; it doesn't change their vote.

Whereas the person making $52,000/year ($39,000 after tax, $51,000 after the UBI) is not going to be inclined to go from $51,000/year to $15,000/year even if it meant they didn't have to work, so all of those people are going to want to keep it at $12,000, to say nothing of anybody making more than that.

> Additionally, I can also imagine politicians promising increases to the UBI without concomitant tax increases, funded by bonds or other kind of financial mechanisms for monetary injection whose long-term negative externalities would be easy to obfuscate from voters.

But we have this problem already. It's an independent problem.

If you can find a way to stop it, do it. But if they're going to do it anyway then better that the money goes to everybody than that it goes to whichever cronies have the best lobbyists.