Consider incentives. Under capitalism one incentive is the possibility of becoming rich, but another, more basic one, is the desire not to starve. Under a command economy you won't usually starve (because you're a useful labour unit), at least in a situation where you can do something about it. You still might starve because of incompetence or a political decision.

A large number of people do not enjoy their jobs and, given the opportunity, would... take early retirement, let's put it this way. That's a problem. Command economies solve it by command (recall that being unemployed was a criminal offense in the Soviet Union). Capitalist economies solve it by saying "OK, I'll wait till you get hungry".

A livable basic income would make that incentive disappear. Yes, some people would be happy. The consequences for society, though, are debatable :-/