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UBI will be another government-issued method of control of the population. Government has no money other than what it took from people and companies (well, this is not exactly true, there are government-owned companies, etc, but they don't earn enough). UBI is the wrong direction. Humanity should look into making basic services free and automated, so cost of living goes down instead of being given money to pay for services that government has no control over (hopefully). This is critically important difference and I wonder why people don't see it as it is.

What would be the means of exchange?

Prices will go down regardless as automation becomes more adopted. The question is who will own this automated economy. Whether basic services are free or have a cost, the general population will be dependent on it. By adopting UBI, you give the people an equal opportunity to participate in the free market, thereby having an economy more representative of the needs of the general populace.