One of the problems we face is NOT a guaranteed job for everybody: What with automation and AI there simply will not be enough 40 hour per week jobs that serve any useful purpose. The Basic Income will be so we don't have to get everybody unemployed digging holes and filling them in.

Giving some money to these unemployed people is supported by the Laffer Curve idea. It simply extends the curve into negative regions. When you give money to poor people they go out and spend it all immediately and it bounces around the economy many times. Some of it gets paid in sales taxes, some in wages to people who do have jobs and thus it generates income tax. In fact, if it bounces around enough it ALL gets paid as one tax or another, so it comes back to the government.