Salmo,
I tried to prosecute for embezzling, the county refused even look at the evidence. All she did was collect the mail, sign the checks that came in into her own name and walked out the door at the end of the week with $10,000 of my money. I sued and won a judgement. Big deal. Now I was out more. Luckly she got her life together and had to pay me back when she went to buy a house later on.
Sometimes its not that easy to fire someone. If they are union it can take forever to prove they are not doing their work or shouldn't be driving a vehicle. Without drug tests to back you up, it could be near impossible.

Anytime an employee gets into a truck, the employer can be held liable. To say an employer can't take action to protect himself when he is liable is unfair. I also wonder what the liability to a employer is if he suspects an employee and does nothing and the employee hurts himself on the job. In reality, there are few jobs out there where an employee cannot put his employer at risk through drug use. An engineer uses the wrong calculations and noone catches them until after a project is started or something goes wrong. A fast food worker thinks it funny to toss something into the deep fryer that then explodes. A teacher or caretaker leaves some pills around and a kid steals them and overdoses. A doctor or nurse makes a mistake. Part of owning a business involves taking on risks, but it also requires a person to take means to minimize them. Suspecting drug use may not be enough to legally allow an employer to take action (and shouldn't be), proving can be.

I am not suggesting that anyone who uses drugs is a bad employee or a risk, only that some drug use in some people can have that effect. It should be up to the employer to decide what risks he is willing to take and the employee what he or she should put up with. In the case of government workers and large corporations, the unions have a big part in what is allowed. In smaller industries, the employees have a choice of leaving or starting their own companies.

In employment, I do not feel this is an intrusion into private affairs. It s harder in terms of other government services and such. Most people would agree that a drug test for marijunna would be unreasonable to get a drivers license, but what about evidence of a heavy heroin or crack cocaine addiction. What about for foster care, adoption or running a daycare. I think most people would like to know if the person taking care of their kids is a crack addict or Meth addict. And don't think it is that easy to tell. It often isn't until the very end. The whole question is a murky one. I for one am against any testing other than for employment purposes, but can easily see arguments going the other way.