Not necessarily. Whilst we haven't had people caught out by drug testing (either because they're too clever to get caught, or just because they don't do it - and I can believe it), we have let people go owing to performance issues.
Furthermore, I don't believe that that's accurate, though if it is, I'm sure it can't last long and why do that to yourself? Furthermore, being tired and performing badly is just as bad as I said.
I really don;'t see what the big deal is. Employers have every right to protect their image, their workforce, and deal with their codes of work in any way they see fit.
If you don't like the idea of being drug tested, either stop taking drugs, or find another job... fairly simple to me.
If people are trying to defend taking illegal drugs, yet fighting a legitimate lawful test - it's pretty ironic, non?
I know I know, I sound a little "hollier than thou" (thought I'd get the comment in first), but I have no sympathy for people who feel the need to take drugs and lose their job over it I'm afraid. Sure, I can only judge by my own moral code. I've been naughty in my youth so I can completely relate, but as a reasonably mature responsible adult, earning a living and developing my career is more important to me than getting drunk/high/etc...