This is your Big Lie. It's actually so big, it's obscene. Because every decision every human being has ever made, and ever will make, is made through the comparison and evaluation of harm. Every one. The reason being that everything is, one way or another, harmful. And so the extremity of one harm is INDEED used to justify, or not justify, another harm, all the time - constantly.
You have no moral position in this matter. Zip. And even worse, you know it.
Once again, you don't like being called out on the fact that you are proposing to justify the carnage of marijuana by pointing to the carnage of alcohol. It rankles you that I can sum up your position so accurately and succinctly, and it's very uncomplimentary.
As a matter of fact, it sounds exactly like a child's "Well *HE* did it too!" argument, because that is exactly what it is.
"Alcohol did it too!"