I still can't see exempting pilots from screening entirely. Even if you assume they could crash the plane anyway (ala Egypt Air 990), they could still act as a witting or unwitting mule. "Put this package in the men's room, and take the $10,000." Would you trust foreign pilots as well?

Screening of airline staff started with PSA 1771 in 1987. Prior to that, airline employees could enter the secure area without a check.

After being fired, David Burke took a gun on board and murdered the flight crew. The plane crashed killing him and everyone else on board. I don't see any of the people listed as possibly being exempt that would also be exempt from going whacko like this.