"What about all those people who will just spend it on booze and lay around? Why should we support them?"
Such people are a tiny minority. Most people want something besides booze to occupy their time and that means work of one type or another, whether managing a garden and selling surplus veg or developing a skill and producing handcrafted items that last a lot longer than machine made items, or fixing things that break down. Others will be backyard/garage tinkerers who traditionally provide the next wave of technology and entrepreneurship. People want to work. They just don't want to be treated like part of the machinery.
For tiny minority who have no interest in doing anything but staying drunk and loafing, have you ever worked with any people like that? They are a disaster on the job, causing accidents, shoving work off on other people, and generally gumming up the works. There are some people out there who, for one reason or another, just don't get it and never will. It is better for all of us that we stop trying to force them into things they are not suited for, and Christian compassion (even if we're not Christian) dictates that we don't allow them to starve if they can't be forced to conform.
40 hour work opportunities are going to be sharply curtailed in the not too distant future, both through improved automation and AI. A lot of the jobs were physically destructive and soul-suckingly boring and won't be missed. There will be a lot of people out there with no means of support without them and we're not all qualified to be technical staff in charge of repairing machinery that breaks down. The alternative to the UBI is mass starvation and mass starvation leads to violent revolution. The UBI is cheaper.
Even ancient Rome knew all this, which is why it had a basic bread ration for all its citizens. The UBI is not a new idea.
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