It's supposed to be unconditional right? that's why there's Universal in the name. However in my humble opinion, there needs to be a strict criteria on who should receive it. The money should go to all the people struggling to fulfill basic needs, not the upper middle to high class people. I said upper middle class because that'd make some of them to just go ahead and retire no matter the age, which will cause a shortage of productive humans, slowing down the economy. If it's just one country, maybe the impact wouldn't be big but if it's implemented to others, especially to countries where their birthrate are declining, the numbers of unproductive people might spike up significantly. Nowadays, to newer generations, marriage and having children are not priorities anymore. If they have enough money to get by every month, plus a decent amount of savings, they'd just retire and be unproductive. I know I would.
But... that is if we go by the state that we're in right now. But if one day, robots take most jobs to the point where humans are threatened, then UBI should be implemented 100%, world wide even, including for upper middle class people. Because at that point productivity shouldn't be an issue anymore. It's how to make sure humans keep on living and benefit from technology. Robots should make our lives better and not worse. If they generate money, move the economy and it's humans that get the money then it doesn't look so bad. This is my dream scenario and I believe one day it will happen. It's the only way.