I'll miss something, even by numbering these:
1) Law and morality do have a lot in common. In fact, one of the common critiques of American law is that is too influenced by morality, rather than necessity. That is, typically, a critique made by those who want to reform, or largely eliminate marijuana laws. You're one of the first people I've ever see remark that they can't find much morality in law. This is not as personal a shot as it may sound, but you probably aren't as familar with morality as others, who can find it more readily.
2) I do feel much the same way about alcohol and marijuana. Each impairs the user, but in different ways. I think both should be legal. Surprised? Maybe you are, but I also think the use and users of both should be regulated. Your comparison to alcohol is a tired argument, that at best, eaks out a two wrongs can make a right niche for you rhetorically, unless you have some kind of limitiation on the users of each.
3) Hospital lab worker, yep, don't be drunk, don't be high and don't cheat on your drug test to get or keep the job. That's cheating, that's immorality, a my wants over your safety kind of trade off that he's willing to make for himself, but that none of us should permit.
4) Of course I know lots of people smoke pot and work successfully. There's also people who drink alcohol right on the job and do just fine. I really don't care if my canvas artists, trumpet players, ad agency promo brainstormers, or apple pickers are high or drunk, but I sure do care if my pilots, automobile drivers and hospital lab workers are.
5) Neither you nor I know anything about the OP, except what he told us. He may say all kind of self serving things, even untrue ones, but an admission like smoking pot six days per week is something we have to take as true, perhaps even as an understatment, as the amount per day could be understated. Couple that with the inability to have stopped in proximity to the drug test for his intended career dream first job, plus his near desperate willingness to cheat on the drug test, makes your assumption that he isn't smoking just before work, or would be at it, a fairy tale hope I just can't endorse. Already, he's like the drunk who is hiding the empty bottles, or driving away from the direct route home when he sees a police car ahead, or keeping breath mints/moutwash/rinse on him, and in the car, and by the nightstand, and at work, and everywhere he goes so he can mask his alcohol breath, when needed. Guys who drink too much have the same false conceit that guys who smoke pot six days a week do, they think they are hiding it.
6) I know that marijuana affects many people differently, just as alcohol, but I probably have known 500 people in my life, easily, who were/are regular smokers. Lots of them, with the last joint the night before, were readily different the next day from a non user. Now, much of that is cumulative, not from occasional use, but it's definitely the case for many regular pot smokers. There is a kind of delay factor in their observations, critical thinking and memories that survives into the next day. Not everyone, but many. Save your nonsense about how time limited the effects of chronic smoking are on someone who knows nothing, never been outside their home except to go to school or church. They might think they are learning something from you but you are just being an apologist, hiding a far less appealing reality.
7) You bunch together "doctors, lawyers, accountants, etc." as successful while still smoking pot. Maybe so, but let me draw a different line. The lab tech OP and doctors better be drug tested and clean. The lawyers and accountants don't have the same public safety issue that doctors and medical lab techs do. Put the medical people with the bus drivers and motorists. Put the lawyers and accountants with the journalists and real estate agents.
8) For what it's worth, and somewhat off topic, the guys I knew who smoked a lot of pot the night before a morning track practice did better than the guys who drank a lot the night before. The guys I worked with who smoked pot during lunchtime, while working white collar jobs for the Federal Goverment, were less useful for productive work in the afternoon than those who drank at lunch. Finally, my fellow high school, college and law students who smoked a lot of pot seemed to have pretty low GPAs on the whole, although that isn't necessarily the cause, just something that at least seems to happen together. The drinkers were all over the lot, including several who were top students, who would take a drink or two right before every midterm or final. I'm sure they were what we could now call legally drunk when they cracked open the blue book to start writing. I know of no such coping mechanism that worked for success for students with pot smoking just before a big test.
9) Society needs rules to reward or encourage those doing what is productive and punish or dissuade those who want to do the wrong thing. The drug tests for hospital lab workers are there for valid reward/punishment reasons. Cheating on that test, especialy in the context of the horrible misfortune a patient could suffer, is a full embrace of immorality, of the variety of my wants first/your safety last. The OP can smoke pot for every hour of the rest of his life, for all I care, so long as he then doesn't try to simultaneously cross the line into a role where he is supposed to be protective of others and using his full faculties for their medical safety and health, rather than what's left after he uses a mind altering drug. I hope he gets clean, or picks a line of work where a "bad day" or a "mistake" doesn't lead to someone's death.
10) To OP: If you would lie/cheat/steal to hide and sustain a habit, rather than end it, you need more help than you are addressing. It's already a big problem. Stop it before it grows bigger than you. You still can. Good luck.