* Jobs are not sticky (eg, there are 0 switching costs once you are 'stuck' at an employer)
* Employers cannot change their character or terms (eg, it was a good place to work yesterday, now it has become a bad place to work)
* Employers cannot drag an entire industry or employment segment down (eg, race to the bottom)
* Employers cannot do anti-competitive/restrictive things (eg, you must drive this kind of car, you must work these hours, you cannot work for a competitor, you cannot negotiate on the terms of your pay structure)
I'm generally (and historically; eg, younger me) very sympathetic to the idea of freedom to contract for any terms.
However, it is not a zero-sum game. A previously-unemployed person does not become employed and then be magically better for life. That would assume they would have been unemployed forever had this business not come along, and it would also assume that this business cannot become worse to work for over time or limit one's prospects.
I used to be very opposed to the concept of wage floors, however what's changed my mind has been the impact of unemployment to drag down wages. As long as there is >0 unemployment, there can and will be a race to the bottom in terms of the wages and conditions of marginal employment. This wouldn't necessarily be a bad thing if the employment market was a fixed pie (again, zero sum game), but that's not the way the real world works.