Earlier quoted context omitted.
>Who am I to tell a homeless person that she is legally forbidden to engage in a voluntary, hourly employment contract for less than $15/hr? Someone who hasn't unterstood minimun wage fully? Minimum wage covers exactly this situation: You will have to pay at least that amount, even if the person you're employing happens to be homeless at the moment. If an employer is not willing to pay that, than that's not an issue…
If someone says 'my labor isn't worth 15$ and I know you won't hire me at that rate so I want to work for 10$' they are legally forbidden from this, right?
But that's what I think is good about it!: It sets a baseline for what human labour is worth. Nobody has to say how much (or rather how little) his or her labour is worth. If an employer thinks someone should earn less than that - fully knowing that this wage will never enable this other person to get on in life - than she'd rather not employ anyone.