Not a bad idea; however, Robert Hanssen and John Anthony Walker had security clearances. They went bad. A pre-screened individual that knew how to work the system could go bad too.
Yes, and a polygraph didn't catch them. Your point is anybody can “go bad.” But really, you could go nuts today and murder a random person, so, using the logic that anyone is capable of going bad, you should be groped and inspected daily just in case, as it is for everyone’s protection don't ya know. Do it for the ‘chilren.