Maybe what they meant is that without a wage floor people working for extra cash could take the job for below-living wage rate, outcompeting people who are looking to support themselves fully with the job.

(I don't endorse that point of view, just trying to make sense of their claim.)

I think what the parent is getting at is that by instituting a price floor, you prevent people from providing services whose utility is below the price floor. In other words, if someone wanted to do extra work that wasn't worth much money (but might add up over a longer period of time), they are now unable to do said work because no one will be willing to pay them for it.

Basically, when setting a minimum wage, you end up picking between two groups of labor: those who work for some extra money (think high schoolers and retirees who would like some extra spending money and don't mind doing menial tasks that may not generate much value to earn in) and those who work to live (think unskilled laborers who do laborious work and feel they are insufficiently compensated for it). A lower wage favors the former group because they are able to offer the services for less (and the quantity of labor demanded will increase if the price goes down) while a higher wage favors the latter because they can demand more money.

There are part time tasks that we might want to pay someone to do, but are not worth paying anyone for at living wage costs: The value and the minimum wage don't line up. Those are often the kinds of jobs untrained teenagers did back in the day. If it's illegal to pay someone to do it for a wage I am willing to pay, then it doesn't get done.

It would be nice if it was possible to have a sensible minimum wage for, say, employing someone over 5 hours a week, but have mechanisms that make it legal for someone to do very short term work at wages nobody should ever live on. There's plenty of people underemployed at 15, 20 hours a week, that would love to supplement that with a bit of extra work, even if it was under minimum wage. In fact, in some cultures this happens all the time.

That work would also get done if we had a citizen income that matches that living wage, and we got rid of the minimum wage altogether.

Now, whether the world would be in a better state by leaving work not done but guaranteeing a living wage or by maximizing work done is a matter for debate: Looking at minimum wage laws alone is not enough to compare policy outcomes. Still, the grandparent was making a defensible argument, whether you think he is wrong (and he might be) or not.

It isn't a guarantee of that when you tie it to an hourly rate. Anyone who isn't delivering enough value after the rate hike is going to have their hours cut and is going to have a harder time finding a second job, which is something a lot of minimum wage workers have to do thanks to overtime pay requirements. I'm not saying this as some upper middle class libertarian either, I was still working these jobs just a couple years ago. A 40 hour or less work week for me would have kept me in that position nearly indefinitely. Yet raising the minimum wage much higher than it is now would price the people who are most in need of employment out of the labor market. I know you're probably likely to cite recent wage hikes in certain cities as evidence that this isn't the case, but those are areas where a dollar has a much lower purchasing power than it does in most of the country. A national minimum wage of $12 an hour would have made a huge number of the people I'd worked with at a minimum wage job a liability rather than an asset.

Right, but a living hourly wage requirement that applies universally without exceptions prevents someone with a full-time job that pays a living wage (or perhaps much more than that) from doing side jobs that have a price which would provide mutual benefit to both them and the person paying for them, but only do so at a wage below what would, on its own, be a living wage.

This is a real issue (and it applies to regular old minimum wages even they aren't living wages); its among the arguments for why Basic Income would be a better minimum-quality-of-life support than minimum wage guarantees for the working plus welfare for the nonworking, since it doesn't stop any mutually-beneficial work from being done merely because the market clearing price is below an artificial threshold.

OTOH, even people who recognize that the restriction on some work that it implies is a problem think its a cost worth paying for a living wage guarantee given that its harder to get support for (and, arguably, beyond the level of the economy now to support) a Basic Income at a sufficient level in the near term.

Yeah I could take issue with the term too. At least with minimum wage (which has the same issues wrt a price floor, like many forms of work not being worth the minimum $x/hr the law requires) it's the same at the city/state/federal level you live in so you can properly account for it, and in the ideal case is enough to "live" on so proponents are happy. "Living wage" is inherently more subjective. I can live almost anywhere in the US at that place's minimum wage or less -- if I live like a college student, or a bit worse. It's not enough to support a family on. But too often a living wage gets set at some high price it takes to rent a studio apartment alone in your area and eat out every night, and maybe even support a child. It's just a nebulous term.

I live in the Seattle area where $15/hr is the minimum wage now for the city proper. Sure certain businesses still have another year or two to implement it, and other businesses another 5 or so years, but I'm looking forward to seeing the results over time and how well they match various parties' predictions when the law was passed.