Ok, first off, this post is aimed at AW posters who propose Universal Basic Income or some variant thereof, not at the general “a lot of employers suck” crowd (that I can agree with).
Currency is simply a representation of work done or goods exchanged. Some modern economists have argued the opposite, but that's wishful thinking. A government can print as much cash as it wants, add countless 0's to bills, but in the end, the amount of collective productivity doesn't change with the increase in currency. This has been seen across thousands of years of human history, ranging back to early civilizations like the Greeks, Egyptians, and Chinese. Economies resist top-down control, even creating black markets to meet customer needs when governments overreach.
The law of Supply and Demand holds true. A government can print more money so that citizens can buy more bread, and bakers may even try to bake more to compensate, but in the end farmers aren't going to magically grow a lot more wheat for flour without resorting to ecologically destructive practices. So ingredient prices rise, making bread more expensive (inflation) and pricing out a lot of the people who were just handed free money.
Any positive results from limited UBI experiments are due to the fact that it's limited. There's still a massive capitalist economy supporting the individual city or neighborhood getting UBI, similar to how a large population of organisms can sustain a limited amount of parasitism without any major effect. Truly-Universal UBI, though, would be unsustainable, overwhelm the economy, and destroy it.