Unfortunately, the real minimum wage is always zero, regardless of the laws, and that is the wage that many workers receive in the wake of the creation or escalation of a government-mandated minimum wage, because they lose their jobs or fail to find jobs when they enter the labor force. Making it illegal to pay less than a given amount does not make a worker’s productivity worth that amount—and, if it is not, that worker is unlikely to be employed.

Basic Economics: A Citizen's Guide to the Economy