Timothy Taylor summarizes some recent and not-so-recent research showing the surprising extent of occupational licensing.
My own guess is that the politics of passing state-level occupational licensing laws is driven by three factors: 1) lobbying by those who already work in the occupation to limit competition; 2) passing laws in response to wildly unrepresentative anecdotes of terrible or dangerous service; and 3) the tendency when setting standards to feel like more is better. But in a U.S. economy which is hurting for job creation, especially jobs for low-income workers, states should be seriously rethinking many of their occupational licensing rules. Many would be better-replaced with lower standards, certification rather than licenses, or even no licenses at all.
One approach I would like to see is one in which being in licensed in one state means that you are licensed in every state. State-specific licensing requirements strike me as violating the spirit, if not the letter, of the Constitution’s provisions protecting interstate commerce.