Those may be the very same people who play music, build stages or give water to overly wasted kids at summer festivals. Or they might fix your motorbike better

Those may be the very same people who play music, build stages or give water to overly wasted kids at summer festivals. Or they might fix your motorbike better and cheaper than your local mechanic if you asked them to. Or they might not. Either way, I wouldn't consider them any more harmful to society than those probably millions of people working very hard to shove ads into peoples faces ever more efficiently, or those bankers and accountants looking for loopholes to effectively steal from others. Or corrupt politicians whose only concern is filling their pockets. Or I could name a bunch of other mostly useless leech industries. My point is, I think you are judging these people from a faulty perspective very much ingrained into our society, where one's usefulness to humanity is primarily judged based on how much money they can get their hands on either by stealing from others or selling their freedom to someone willing to pay for it, regardless of what value they actually contribute (if anything) as long as it's considered legal and they do so as part of the so called "workforce". UBI would fundamentally change that by allowing people to spend time doing things they consider useful, rather than working for whatever gets food on the table, however useless it may actually be. Of course, for that to work, people need to be open to other people's ideas of useful and the currently dominant view of measuring usefulness in GDP or whatever may become obsolete.