A bunch of people could maintain their standard of living without working. Why would they choose to work? It's not like they are doing things they would enjoy doing.
Almost nobody who does a job that couldn't be automated would have anywhere CLOSE to their current standard of living if they accepted a reduction in total income to the level of any proposed UBI, by quitting their current job as soon as UBI was introduced.
There would, of course, be a need for the wages for truly unpleasant jobs that cannot be automated to increase very sharply indeed, but that's a feature, not a bug. If a job is unpleasant but necessary, it should pay well. It shouldn't pay poorly on the basis that people will have to do it for shit money in order to avoid starvation and homelessness.
The entire point of the excercise is to shift payrolls from funding basics plus disposable income, to funding disposable income only, with basics already covered for everybody.
There's plenty of incentive there for people to work. Just no incentive for them to tolerate having their wages driven by a race to the bottom; So nobody's gonna need to put up with shit work for shit pay.
You want people to do shit work, you're going to have to compete for them financially, without the threat of penury.
It seems to me that this effect of UBI would also enable government to remove the minimum wage. In Australia we could probably do away with all of the pay scales set out in industrial awards, and let everyone's pay be determined by the market.
Employers would be free to offer wages as low as they want, and if they can find people who are willing to sell their labour at that price, that's good for them. Some industries might be able to hire workers at extremely cheap hourly rates. UBI ensures those workers are still able to pay their bills and quit their job if and when they decide the pay is too low. The services those companies provide would also become cheaper.
Other employers may discover that they have to pay a much higher price to get people to work their shit jobs, or change those jobs to make them less shit. For example, Amazon wouldn't be able to treat its warehouse employees so poorly, because nobody would work for them. It might just mean that it takes an extra day or two for the your book order to ship. Some companies would probably go under if they lost their access to unlimited exploitative labour. Their departure from markets would make way for (smaller) companies with a different approach to work with a focus on pleasant, safe and fulfilling working conditions for blue-collar workers.
It's possible that some of the accomplishments of industry that we've witnessed, such as just-in-time logistics and cheap cutting-edge gadgets, might not be possible without the exploitation of workers. But I'd like to see what people accomplish if they aren't trapped in shit jobs.
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And economic measures like GDP growth don't mean a fucking thing if that growth isn't actually providing a benefit to people. What good is GDP growth if people can't even find a job that pays the bills?