Minimum-wage laws make it illegal to hire a low-skilled labor for their market value. This makes it more difficult for the less-skilled to acquire skills and get on the low rung of the economic ladder. Minimum-wage laws also inhibit the division of labor, which inhibits capital formation and hurts society as a whole.
And the one thing that no one seems to point out but that bothers me is this: how are price floors (such as minimum-wage laws) violative of the first amendment to the constitution? How is that not a violation of free-speech rights? Prices convey information--speech. But you are not allowed to convey certain information--wage price below the minimum-wage rate--and if you do anyway eventually the state will throw you in jail. That violates the first amendment, plain and simple.