Occupational licensing hinders job mobility

I'm an MD, and I have felt this pain moving from one state to another. I've never had a problem getting a license, but it's tedious and expensive, and then there's always the question of whether or not to keep a license after moving (which generally just means keep paying them money forever).

Getting doctors to agree about anything is nearly impossible, so a national approach to licensing has patchy support. Some feel that if they are the subject of an unfair inquiry (which is not standard but sadly not uncommon), they would have no recourse if there's a single licensing body.

What is the right balance of licensing?