I found the process of getting a mere "Secret" clearance in 1985 and again in 1991 pretty invasive, enough so that I don't believe I would take a job that required any clearance. I'm not a shady character at all, but having old friends call you up and say that a sweaty guy in a suit is asking questions, and then telling you "I spilled my guts" is not a good experience. If you get a clearance, your family and a lot of old acquaintances are going to have brushes with The Law. This may not be a good experience for everyone.