Plenty of thing in life are achieved by people working for free in association and other things. Consumer and citizen association are working for a long time in history to makes everyone life better. Not everything can be ruled by economic insensitive. Some things dont generate money , like safety , laws , regulation , most of research and very niche technology. Some exceptionnaly rare disease wouldnt have any research advancement until some very rich kids get it , some technology for disabled , sick people wouldnt exist without being subsided.

Some book , art , tools wouldnt be created without some people being born from rich parents, because they wouldnt be able to do anything else than work otherwise. If you acknowledge that , you can understand that an universal salary would profite not only for the poorest , but also for everyone else , with more research, creation and devellopment being made by everyone and not only rich kid that got time and money.