There is a massive chasm between wanting, desiring, and helping people to make good decisions about their life, about their body, and about their choices, as compared to a compulsion to make certain choices or to forego activities that fit a particular construct of the government or of private enterprise which doesn't taken into account your background, or your social economic level, or the arbitrariness of the desired action itself. I absolutely detest mandatory drug tests in any situation in which you have not been found guilty of a crime that would necessitate you taking such a drug test now or in the future.
A man's right to privacy is part and parcel of life, liberty, and the pursuit of happiness, and should not be infringed upon, even ostensibly for good reasons to do so. While you can make an argument that for people that have jobs that required the operation of heavy machinery, or the driving of vehicles, should be tested for drug use, that presupposes that having some sort of trace of drug usage within your body is proof positive that you are impaired, incompetent, and a real and present danger to yourself and to other innocent people. That may or may not be true, it is absolutely situational dependent, and to paint broad paint strokes that put all people that have a certain arbitrary amount of trace chemical in their body as impaired is a step too far.
Additionally, if the real reason that drug tests are conducted is the protection of the general public at large and for the safety of the individual itself, the test and test result must be done in real time. For instance, using an accurate breathalyzer or similar instrument which is both calibrated correctly and efficient in processing the test results may be something that is worthwhile in certain specific circumstances.
The main issue that I have with mandatory drug testing is the grouping of everyone into "guilty", unless the drug tests exculpate you, which is exactly the opposite of what this great country represents. There are also the issues of privacy, of stress, of inconvenience, of cost, and of accuracy which makes these sorts of tests very suspect. Furthermore, it follows that if you allow or continue to allow mandatory drug testing, you are one significant step closer to mandating brainwave testing or similar, again for the safety of yourself or others. The point of the matter is once the State determines that it can test you for one thing, it will invariably want to test you for everything, and those that do not meet or satisfy some pre-determined ideal that the government desires will be ostracized, marginalized, and turned away.
Drug testing is really one of those things that are setup to separate the "elite" from the commoners, in which the elite will never fail such tests because they are the ones that establish the rules of the road to begin with. The commoners will always be a step behind, under assault, under a microscope, subject to unemployment, banishment, or rejection at a moment's notice; so that their hands are tied and they are placed into a situation in which battling the establishment is an exercise in futility, they will instead simply be used as a tool that enriches the elite and for the recalcitrant ones subject to the elite's disposal or cleansing.