This is only holds true if there are more jobs than workers and working these jobs is preferable to unemployment. The reality is that the vast majority of workers are dependent on the decisions of whatever corporation will take them in order to maintain some standard of living.
In your example if we had no unemployment safety nets at all then any form of labour would be justifiable because some workers would choose it over begging/starvation. In fact it is this very argument that is used to justify why people should be allowed to sell themselves into slavery. I believe the preferable alternative to this is to improve those safety nets such that people are able to make a choice on whether that work is worth doing, free from coercion.
> But in a situation where some companies offer shitty conditions, and lots of people decide to go away from their existing companies and work for the shitty companies, then you have to at least entertain the notion that you were wrong about what makes a job shitty.
The problem is that if those shitty conditions allow the company to outcompete, competitors are eventually forced to match those conditions. If we get rid of labour regulation and I start employing children for £0.30/hour my competitors are forced to take a similar step or I'll destroy the majority of them on price alone.
The gig companies do exactly this by shifting the risk of loss on to the worker and relying on information asymmetry between themselves and the worker on the effects of worker competition in order to retain them. In models of traditional employment the company hires and schedules its workers based on forecasted need. If the company mistakenly hires more workers than needed they suffer a reduction in profit. If a gig company "hires" too many employees, the employees make a lower hourly wage and the company increases customer satisfaction due to quicker delivery/ride times. This shifting of risk is what makes gig companies dangerous to the existence of other jobs regardless of whether they're preferable in other ways.
Gig companies are directly incentivised to maximise the "supply" of workers which results in a situation where each additional person signing up reduces the potential earnings of participants in the same area. This is advantageous to the companies but not the workers and that's something that isn't immediately obvious, we have to hope that enough people realise before it becomes the only option.
What makes this even worse is that these companies are burning huge amounts of capital dumping prices/inflating payouts in order to disguise the true costs of their business. The result is that stable businesses are squeezed out artificially.
> In that sense, having some companies with shitty conditions offers an important safety valve to learn that regulations were misguided.
This wouldn't tell you that regulations were misguided unless they happened to be in violation of those regulations. I think that while imperfect public opinion/democratic vote is a much better option than "the invisible hand" for deciding which regulations are valuable.