Take Warren Buffet. Did he really contribute 76 billion dollars worth of value to society? I don't think so, and I don't think even Buffet himself does (he has said that to spend his vast accumulated fortune on himself would divert resources from important things). But once you make beyond a certain amount it's almost hard not to make more, without doing anything at all! Here's[1] an interesting personal account of this on our very own HN.
Conversely, someone at the bottom of the ladder can work 60-80 hour weeks in multiple jobs and barely make ends meet, let alone save.
I would even argue that an unemployed person actively seeking work is probably contributing various forms of value merely by existing - most obviously in the form of liquidity to the employment market, but also in all the other ways a living person is valuable - they listen and talk, make friends, form opinions, vote, and otherwise reinforce the fabric of society (hence why it is still a tragedy if such a person gets hit by a train, and a crime if they are murdered).
Moving further down still, when push comes to shove, most people would agree that even the most miserable, useless wretch does not deserve to die, if the resources for their survival are readily available. There is value, moral value, in compassion. A society that takes this view is spiritually wealthier.
So you have a scenario where, monetarily, the people at the top are systemically overvalued, and the people at the bottom systemically undervalued. This seems to be a deep property of the system that can't be fixed by fiddling taxes within the existing framework - money trickles up, where it accumulates. Closing the loop with a basic income, even a nominal one, is a direct and practical solution that doesn't have to hurt anyone.