In fact, the minimum wage is very good for unskilled workers. It transfers income to them. And therein lies the right argument against the minimum wage.
Ordinarily, when we decide to transfer income to some group or another—whether it be the working poor, the unemployed, the victims of a flood, or the stockholders of American Airlines—we pay for the transfer out of general tax revenue. That has two advantages: It spreads the burden across all taxpayers, and it makes politicians accountable for their actions. It's easy to look up exactly how much the government gave American, and it's easy to look up exactly which senators voted for it.
By contrast, the minimum wage places the entire burden on one small group: the employers of low-wage workers and, to some extent, their customers. Suppose you're a small entrepreneur with, say, 10 full-time minimum-wage workers. Then a 50 cent increase in the minimum wage is going to cost you about$10,000 a year. That's no different from a $10,000 tax increase. But the politicians who imposed the burden get to claim they never raised anybody's taxes.
If you want to transfer income to the working poor, there are fairer and more honest ways to do it. The Earned Income Tax Credit, for example, accomplishes pretty much the same goals as the minimum wage but without concentrating the burden on a tiny minority. For that matter, the EITC also does a better job of helping the people you'd really want to help, as opposed to, say, middle-class teenagers working summer jobs. It's pretty hard to argue that a minimum-wage increase beats an EITC increase by any criterion.
The minimum wage is nothing but a huge off-the-books tax paid by a small group of people, with all the proceeds paid out as the equivalent of welfare to a different small group of people. If a tax-and-spend program that arbitrary were spelled out explicitly, voters would recoil. How unfortunate that when it is disguised as a minimum wage, not even our Republican president can manage to muster a principled objection.