[nkurz]

I think the difference is the seemingly artificial restriction on the supply of labor, and the assumption that if there are qualified individuals willing to do the work for less cost, they should be allowed to do so. If the employers are blocked from hiring these others by those who are currently employed, this strikes many people as unfair to both the employers and to those willing to do the work for less, as well as to the public who in the end bear the extra costs of the inefficient labor market.

The presumed difference with white-collar work is the assumption that this pool of willing and qualified workers exists. Maybe it doesn't? I'm guessing that while there are many people who could be trained to be excellent computer programmers, but I doubt there is a significant pool of ready-to-go programmers in Oakland who are being blocked from employment by the current programmers currently holding a limited number of positions.