I don't think that the only thing keeping civilization together is the fact that a certain population is impelled to work by starvation.

If the prices of things are being kept artificially low, due to the duress of the employees producing it, then the market will fix the problem. We might see a short term rise in certain commodities. But, unfettered, this just induces more efficiencies, such as automation, into the system. Efficiencies produced by upper middle class engineers, who would now, thanks to UBI, have the same earning power as their upper middle class parents did.

UBI isn't wage inflation for many reasons, such as the actual value of money isn't equal to people with different incomes. It isn't going to become more expensive to live, because people don't go out and buy twice as many groceries when the have twice as much money - the money is used for different priorities.