I think the main reason large companies like substance testing is it's "objective" information. So much in the hiring process is subjective and in a big company the people that run it doesn't hire most people, or even someone just under them, but down many levels. But there is at least the problem that they don't weigh the information against other attributes. That and what they usually find is that the person is clean OR cheated the test. Great.
I think those who don't do anything should be most insulted and unwilling to submit to tests, however they often lack principles due to no reason to think critically about them, plus they don't like us.
As to being libertarian, I find the argument for isolated libertarian practices in a nonlibertarian society lacking. E.g. something like Obamacare is necessary in a repressed economy.
OMG I liked Ninja's last post.