So a job that advertises terrible working conditions is suddenly morally upstanding and ethical just because you know what you're in for? What if you need money to feed your family and the job ad says that as a precondition to getting hired you need to give them one of your kidneys?

This is exactly why labor law exists and why libertarian/extreme capitalist societies could never function. The argument "it's a free market" doesn't hold water. Without a system of checks and balances exploitation will always take place because there are always people desperate enough to do anything to make a living. No matter what you say about "free markets" and "voluntary agreements", you can't convince me that it's right and ethical and a good idea in any capacity.

Just because accepting a job is voluntary doors not give license to employers to exploit their employees. 100 years ago, that same argument was advanced by people opposed to worker safety laws and child labor laws. People use that argument to justify jobs where you have to sleep with the boss to get the job. The fact that some people are desperate doesn't give an employer endless license.

That some naive person "volunteers" to be exploited and abused doesn't make it any less exploitative or abusive.

Unemployment is really high right now. A lot of folks might feel compelled to take any job.