It is all about needing the money - or rather who has the greater need - you for the money or them for your skills.. I've taken a piss-test exactly once, when I was only a few years out of school with little money in the bank. Since then, any time the issue has come up, I've said flat out that it is not an option under any circumstances. I'm so straight I barely drink any alcohol much less indulge in recreational pharmaceuticals, but I believe the "war on drugs" is responsible for more damage than good (and paved the way for all the bull**** that is now the "war on terror").
When even the US government does not require a piss test for a secret clearance it seems way out of line for regular commercial companies that are nominally white-collar employers to do so.
I've been fortunate enough that in each case their need for my skills was great enough that they ended up figuring out how to hire me without requiring the test and I like to think that in the process I've been able to use my clout to get some people to think about how pointless and invasive their corporate policies are. I'm sure that some of them just figured I was a long-haired druggie or an reasonable idiot for refusing to go with the flow, but as George Bernard Shaw said, "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man."