No man is an island, as you say, except I guess if your drug of choice is alcohol, then that's okay.
Here's a hypothetical for you:
The two units of a duplex apt. are rented to single males, around 25 YO, with similar jobs and incomes. The guy in unit A gets drunk every night, the guy in unit B gets high on pot every night. Morally, they are engaging in the same behavior, using drugs to alter their moods. But legally, they are treated differently. The guy in unit A can get drunk every night of his life and the police won't bother him. However, as you well know, the guy in unit B is in trouble with the law whether he smokes pot 7 days a week, 7 times a month, or 7 times a year. Their behavoirs are morally equal, yet they are treated differently and unequally before the law.
The simple fact of the matter is that you and your ilk are making distictions in the law when the underlying behaviors are the same. That is injustice, there's no denying it.
Let's face, you and your ilk support injustice in the law. I just wish you'd be honest enough to admit it.
You can't let logic get in the way of an emotional response.