A minimum wage discourages the formation of labor cartels as such a potential cartel can't reduce wages bellow the minimum.
Disallowing workers who choose between low income and unemployment to earn low income (thus forcing them to unemployment) can hardly be called protection.
A minimum wage hides unethical businesses from prospective employees. Pay is one tool an employee can use to evaluate prospective employers.
If an employee agrees to work for the salary offered by the employer, then it is not an unethical exchange.