If it makes it impossible for me to fire you because you are smoking pot as a result of productivity loss, it's impeding on my rights, sorry. The California law would have made it "discrimination" to do so, which is just ridiculous.
"If someone gets high all the time and is able to produce amazing output, then why would you fire him?"
Do you want someone under the influence flying airplanes, driving a school bus, or operating machinery that could potentially harm others? Seriously? I've seen enough people high to know how scary a thought this truly is.
"The only thing that should matter for you is how useful they are to you for a given purpose."
Right. Because a drug that many times causes short-term memory loss and paranoia is going to help someone's productivity.
"Reality is harsh. People try to cope with it with their own tools. Different tools work for different people. Drugs are such tools."
It's funny because you are so dead set on freedoms and rights. But when your rights take away the rights of other people, you see no problem with it.