So the company is violating your privacy rights because it doesn't want somebody who regularly takes drugs to work for them? If you don't like it, quit. The company has rules and policies - if you think they infringe on your "rights", quit. Simple as that. Better yet, don't become an employee of that company in the first place.
As well, as others have said, high-functioning stoners tend to think they aren't impaired, so they come to work stoned. I don't know about you, but I don't want to work with somebody who's brain is purposefully altered by chemicals that change the way you perceive and react, legal or illegal.
Quit, to prove what? my company was bought by a big player who changed the rules, why should I dump myself on to a crappy job market, myself and other were the ones that helped keep the company viable so they can make a nice profit on it's operations. Due to the ongoing huge profits made by the likes of Labcorp and Quest, you can be expected to be drug tested for any job nowadays. Their lobby is so strong and drug testing is a %75 profit for them so they spread fear and misinformation (yeah, safety studies THEY sponsored) to keep up the cash cow. People like you would like a society of sheep that bend over when corporate America tell you to, even if you don't or will never use drugs your a gutless coward to not stand up for your rights..