For me, it boils down to two questions: 1) Given, that let's say only 20% of the population does real work (doctors, teachers etc..), why should they do their work, if everybody else is enjoying spare-time all the time? And if you propose that they also could work less, therefore we would have more doctor positions to be filled, guess what, people that have valuable jobs are also the ones who really like their job, and are happy with working 40 hours, or even more. It's somehow ironic that people won't do work, just because they like what they do, they also want to be acknowledged monetary, no matter how much they like their job, which I can understand. Somehow we have a situation, i.e. from a doctor's perspective, like: "Yea, I'll treat you, but only if you are also getting up at seven every morning and commute to some office and do stuff."

2) I think for biological reasons, people need status more than spare-time. We need some kind of hierarchy to determine who is more entitled to spread their genes. If everybody is unemployed, how do you know who has more status? Money and consequently buying power does simplify this problem very neatly, reducing it to a one-dimensional metric scale, easy to compare and communicate.