"It makes greedy capitalists pay people the decent living wage they deserve!" At least that's the most common benefit people cite for a minimum wage. It falls apart though as soon as you realize that there's no such thing as a free lunch.
The purpose of a business is to make money. A business that fails to make a profit is one that goes out of business (barring bailouts from government). Businesses must pay their employess less than what an employee's work is worth. If they paid employees more than they are worth, it would be a charity, and the revenue the business generated would not be able to sustain the business over time.
A person without skills cannot produce much, therefore their work isn't worth much. Say a person's productivity is only worth $7 an hour. As of 7/24/2009 fed min wage has been reset to $7.25. The regulation didn't increase the employee's productivity, it just made it illegal to pay him what his productivity is worth, and therefore cost him his job.