The best argument for UBI is that we already have it in some form. Most modern nations have lots of issues but the poor starving is not one of them. In fact, obesity due to over consumption seems to be correlated with (relative) poverty in many countries. The reason for this is that we have all sorts of safety nets that collectively mean that you are taken care of one way or another. Food, shelter, and to some extent health care are pretty much taken care off in most countries. It's almost universal with some notable exceptions.
Introducing UBI properly is basically just simplifying the status quo and has useful side effects in the form of it being overall cheaper, simpler, more effective, and fairer.
More importantly, it can act as an economic stimulus as well. Yes, there's a cost but it's not different than any other economic stimulus. The current corona crisis is basically a good example of governments printing a little extra cash to help out businesses and people. We're talking trillions here. Economies are not closed/circular systems and increasing the supply of money is routine. The role of central banks is to control the rate at which we print new money to keep inflation in line with economic growth. So people waiving the cost argument without considering the benefits are being disingenuous. Bailing out a bank is no different than bailing out an unemployed person. If we can do one, we can do the other. And we routinely bail out banks and other industries to the extend of trillions.
From an economics point of view, more people with disposable income is actually great because it increases spending. It's a particularly effective form of economic stimulus. Perhaps more effective than bailing out a few wealthy individuals could ever be. The current model of all the wealth accumulating with a small group of people is actually bad because while they spend some of it, a lot of the wealth just disappears abroad via off shore accounts, spending in other nations economies, travel, etc. Increasing incomes at the bottom by a few percent on the other hand basically feeds almost entirely in the local economy. People spend it and they mostly spend it locally benefiting local businesses. You could argue that our current system of sucking the lower classes dry so we can provide tax benefits to the rich is actually killing our economy and is actively harmful. This form of reverse robin hood style handouts is not new either. It's basically how feudalism used to work. Capitalism is reverting to feudalism.
The argument of stimulating the economy also can be used to motivate raising minimum wages; which of course become redundant with a UBI. This is another advantage because it reduces the cost and risk of employing people for employers. They can pay market prices instead of having to overpay a minimum wage for someone that they have to commit to keeping employed long term. It's a big reason why outsourcing to low wage countries is popular. So, UBI can potentially fix this too.
But again, we already have it. All we're talking about here is how to do it better and get more economic effects out of it.