UBI gives someone something without them having earned it. That is the root of the wrongness here and why I am completely against it.
The current system of welfare gives people something without earning it, but worse, it creates perverse incentives: attempting to earn their own way results in the loss of their handouts. Why would they even try?
Under UBI there is always an incentive to work. UBI only guarantees a bare-bones poverty lifestyle. People want to live better than that. They can get a job, and every dollar they earn improves their standard of living, and their income taxes reduce the net amount they receive from the government.
The neat thing is this eliminates a whole slew of poorly-conceived government programs: welfare housing, food stamps, minimum wage...
Eliminating minimum wage is a big deal. Every business owner knows there's a gap at the low end where they'd love to hire more workers, but they can't afford them. UBI eliminates that gap. Instead of mandating a salary sufficient for food and shelter, businesses can hire workers for a wage that matches the value they provide. Even at $4/hour, every dollar the workers earn helps pull them above the poverty line instead of trying to climb back up to it.
This is better for everyone than the current system: it eliminates bureaucratic welfare programs which are an inefficient use of taxpayer money. It helps businesses hire more workers. It's more humane for the poor.