It takes less than four hours to run a sizeable distillation. It is not reasonably possible to prohibit such an activity, which can be carried on indoors, with no outwardly visible signs (energy or water expenditure, for example), using legally-available materials.
Nevertheless, the state still outlaws private distillation, even for personal use only. Even though hard liquor is legal.
Why keep pot illegal? I’ve argued in this space before that one good reason is that pot is an enivronmental intoxicant. Legalization and public consumption of marijuana will inevitably expose innocent people to the smoke, as innocent people are currently exposed to tobacco smoke. Worse than tobacco, secondhand marijuana smoke can have intoxicating effects. You would have to be extremely sensitve to THC to show intoxication from passive inhalation. Here’s a summary of a study that claims that passive inhalation in a social setting (i.e., not hotboxing) should not cause a positive test result.
I’ve also argued that valid conservative reasons — avoiding disruption to settled social customs — exist for keeping marijuana illegal. What is the mainstream etiquette for smoking weed socially? There isn’t any. We’d have to develop it. What an annoyance. Libertarians may find this a weak reason, but it’s a serious claim. Conservatives stand against change, unless it’s trumped by social justice. There were, after all, valid conservative reasons to oppose desegregation. They just don’t hold water against, you know, equal rights under the law. (Bye-bye, Trent.)
But I don’t think that marijuana should be illegal pour encourager les autres.