Taking drugs in or before going to a job can be very dangerous. It will provide the law abiding employees with the feeling of safety. If you have drug-free employees, your customers will feel safer and ultimately give more business and opportunities. It would also lead to more reliable service and a safe environment.
There are talented, skilled, reliable employees who on their offtime do drugs, particularly cannabis. If employees are coming to work high then that is a problem but that will be noticed, at least it will be noticed that their work is getting shoddy or their attitude is unacceptable for the workplace. Without having to test for drugs the employee would end up fired.
But an employee who only does drugs on their own time, and is always sober when they go to work could be an excellent employee. With drug testing you could be keeping good talent away. The famous scientist Carl Sagan was very fond of marijuana. You wouldn't want to fire him would you?
Furthermore workplaces that test for drugs rarely ever test for alcohol, and coming to work drunk will cause an employee's work to suffer much more than if they come to work high on marijuana.
And even without drug testing you may still have rules in the workplace saying employees are not to come to work high on drugs, and that can still be enforced if an employee comes to work clearly smelling like marijuana and with bloodshot eyes.
Furthermore some drugs are difficult to test for, and you may just encourage employees to resort to those, often more dangerous drugs. Every year or so you hear about a new "artificial cannabis" that is legal to sell. States usually ban these, but then a different version pops up later. Even after they are banned this doesn't mean there is a test for it, and people will keep using it if it means a clean test. While cannabis itself is nearly harmless forms of artificial cannabis have turned out not to be both for the user and others around them, so drug-testing may actually be pushing the employee to use drugs that can NOT be tested for which can be bad both for the employee and for the workplace.
America suppose to be free so don't tell what to put in my body. Secondly ever heard of k2 it's much worse than weed and it kills people and so does alchol. Weed is harmless leave us alone. People have died from k2 and other drugs trying to pass
These stupid test. God isn't it a free country or do we just say that for no reason.