The bottom line for me is Marijuana makes people less mentally sharp and less capable while they are under it's influence. They also seem to fall into a lifestyle where they are frequently in such condition. Why anyone would want to do that to themselves is beyond me.
It is good that most jobs have drug testing requirements. People who are high make crappy decisions, have low productivity, underperform, and put others in danger of injury or death.
I can say the same things about alcohol, and I am not one to justify it either. I don't know if someone could have a joint each evening, like many will have a glass of wine or a beer each evening, and have the effects be completely gone the next morning. In the USAF flying world, the requirement was 12 hours between bottle and throttle, and you better not be hung over either. There were many prescription drugs you could not use or be under the influence of while flying. If you violated any of that they took your wings and separated you from the military. Any pot use at anytime in one's life disqualified you from becoming a pilot. And if you were ever caught lying about anything as a pilot, you were done.
I'm sure the USAFs rules on Pot were because of the excessive problems Pot use caused in the Vietnam era. They also cracked down on alcohol use in the late 80s. Recreational and addictive use of substances that diminish your mental ability is always a bad idea.......