Testing for Marijuana is wrong and unfair in the first place. Why is it OK for someone to down a six pack every night and then go to work the next morning, drive all day and, start again the next night? Alcohol is not only psychologically addictive but there is a physically addictive nature to it as well.
Pot, on the other hand, is simply a weed that grows naturally and can be found just about anywhere on this planet. I would agree there is a psychological dependence one can develop, but stopping all use will not give the user physiological withdrawals like alcohol would. While I'm on the topic - I heard somewhere that over 50% of the US population are on some sort of medication. How many people are driving under the influence of some sort of pill? I'd guess a lot of them are. I found a study saying that 9.6% of the population abuses some sort of drug, whether it is legal or not. That's a lot of people.
I guess my point is that it isn't right to drive while under the influence of anything. Pain pills, alcohol, weed, cocaine, etc. It is not only dangerous to yourself but to others as well. Nobody has the right to endanger other peoples' lives while in their vehicle. Whether it is legal or not is irrelevant.
My problem with drug testing is mainly that it is an invasion of privacy. If I were to smoke a joint 29 days ago, it would still be in my system right now. If I were to down a case of beer, take cocaine, extasy (SP), meth, crack, heroin, prescription drugs, inhale toxic fumes, LSD, all of that would be out of my system in less than a week.
Doesn't sound fair to me!