Minimum Wage is also an attempt to keep the employer/employee relationship decent.
You could have a business model in which you maim small children so that they can earn more money while begging for you, but we, as a society, have decided that it is a bad thing. Yes, it happened in Victorian England and present day India, but we don't do it, even if it is "optimal" under free market conditions.
So, requiring you pay a person enough to live a decent live might not be that bad of an idea. If your business model can't support it, maybe you shouldn't be in that business.