> Suppose that it's not, at scale. Then the work still needs to be done, so wage rise until it is enough for enough people.

That's a really big and unfounded assumption. Especially here on HN it's a well-known trope that employers complain that they can't find any engineers when really they can't find any engineers at the price they're willing to pay. Not to mention that there are ceilings for the price of labor - the money for salaries doesn't come from thin air; it generally comes from higher prices. If prices can't raise to the level needed to support the necessary salary, the business and product simply won't exist. Whether this will result, under UBI, in creative destruction, a death spiral for the economy, or it simply won't be a problem at all since people will keep showing up to work anyway, is quite frankly a matter of faith at this point.

> If you give the fisherman the first boat to begin with, he doesn't go out and build a fleet, but he's still a fisherman. But there is nothing wrong with being a fisherman. This is the basic trade off in having social programs at all instead of pure ruthless capitalism.

Yes, there is something wrong with just being a fisherman. When the fisherman starts a business and grows a fishing fleet, the fisherman creates jobs. If the fisherman just stays a fisherman, those jobs never get created. If most people aren't working, you don't have a tax base to fund UBI (or any other social welfare program) in the first place. If people would rather not work, then adopting UBI is more likely to result in the collapse of the economy, not strengthen it.

> Is it "optimal" for people to go home after work and play video games instead of working more?

As a matter of fact, yes, because occasional rest and relaxation is an important part of sustaining yourself in the marathon that is your working years. If you wreck your work/life balance with no end in sight then you're going to burn out pretty quickly.

> What about developing video games? What about growing tobacco, or mining coal, or building bombs? There are a lot more counter-productive things than sitting in a room and effectively doing nothing.

UBI doesn't address any of these issues. They'd all still offer some kind of compensation anyway. If society deems them to be counter-productive, there are other means of countering them - tax policy etc.

> It would be a great improvement if all it did was provide exactly the same level of support as existing welfare, but provided it in cash instead of with strings attached

This is naive. Food stamps are intended to ensure that people are fed. Housing vouchers are intended to ensure that people have a roof over their heads. If you give people cash instead of food stamps and housing vouchers, people will either have food in their bellies and a roof over their heads, or they won't. If they won't then the moral case for UBI no longer exists (because the moral case for welfare programs will no longer exist). If they will then we're back to the original argument over whether UBI will motivate or demotivate people to work. That UBI costs much less to administer is more or less a fringe benefit compared to the risk that UBI poses to crashing the economy.

> If more jobs get replaced by robots

Much hype and lost in transit. Most of the gains in automation are due to growth in technology firms, not robots; most of the losses in manufacturing are due to globalization, not robots. There's little evidence showing this to be feasible.