I think people intrinsically want to be active and have projects and learn and create. BUT you have to detox from living such a structured life, and that's a process that takes time. It's no surprise to me that people who have gone to school or daycare since before they can remember, then had to work full-time after that, don't really know what to do with themselves when they have a few days or a week off, or that they spend that time in ways that appear to be wasted. You need to recover from having someone else tell you what to do all the time. Sadly not everyone does.
On the other side of the argument, yes, this having fun in your free time might just be a way to blow off steam after a mindless, pointless day or year at work. Following this argument, then yes, taking out the boring work from the equation might also reduce or eliminate the need to feed your pleasure side. But I, for one, I'm not really convinced of this. It might still be true, but it's not a given in my view.
EDIT: If you read the end of Gruber's book, there's an exploration of this and the associated moralising.
If we accept the premise that 40% of people add no value to the world in the jobs they have, it seems preposterous to even entertain the thought that none of these people would add any value to society, if you liberated them from their jobs.
The whole open source software movement is proof to his position. People spend a lot of free time delivering value out of hours, value to both businesses and society. Most of these people have a normal day job.
Sure, maybe 1% or 2$ of that 40% would do meaningful work. Let's say we take that for granted. What about the others? What social role would they play? Who or what will pay for their idleness? Who would want to clean up the garbage if a majority of people do nothing and still get payed? How would you explain to someone who cleans the streets the the idle folk might come out with something useful in some distant future? How would the social fabric just not disintegrate? How can you keep the society functioning as a whole?
This is a bit like shoveling snow. I shovel the street around where I live so I can park there. Some people help, others don't. I'm fine with that. I care about it being shoveled so I take action. If I didn't care, then I wouldn't. That's the point.
Fundamentally, playing video games and watching videos gets boring after awhile. People want to be useful once their survival and security needs are met. It is obscured in our society because low wage workers are barely surviving and the bs jobs people, who often make plenty of money, do not have long term security. They know that they can be fired at any moment because they are not actually useful. That job insecurity is what fuels the managerial feudalism and why useful workers are squeezed out (they have the true power to strike).
Much of the population lives below the point where the drive to be valuable kicks in. Implementing a UBI would allow us to potentially get above that point.
No one wants society to fall apart and so it does not. If everything was based solely on money, there would be no kids, there would be no helpful people, there would be no taking care of elderly parents, there would be far more law breaking than there is, etc. Society works because we need it to do so and we will do whatever it takes make this happen.
Hell, I consider my own work reasonably valuable/productive, but if I was free from needing to do it to survive I would likely find something more productive/interesting/meaningful to do.
But also, people who write open source for free in off hours have good marketable skills. They are not in same position as people who cant do something like that.
There is also a lot of work involved in making function software that is just that - a work, oftentimes thankless boring or politically bullshit difficult work that needs to be done and is done by people who feel responsibility or duty to finish it.
How much of the free time development is done, directly or indirectly, in support of their day job though. Often times they're doing it either to improve the tools they use on their day job, improving the skills they use on their day job or trying to learn new skills so they can get a new/better day job.