I would argue that comparing moderate alcohol use with moderate THC use are two totally different things. They are two totally different drugs that work two totally different ways.
With alcohol, you can drink one or two drinks at a moderate pace in a responsible environment, and they it can produce feelings of relaxation without drunkenness. If you are prudent and honest about how you body handles the alcohol, you have not lost control of your faculties of reason.
With THC, the effects are more all-or-nothing. Either you’re stoned or you don’t feel anything. You can take one or two “hits” from the joint and never feel any of their effects. Then on the third hit, BAM! You’re stoned. THC has to reach some sort of threshold in your body before the effects are felt. It would be like from going from feeling absolutely nothing from the first two drinks of an alcoholic beverage to complete drunkenness on that third drink. You have therefore severely compromised your faculties of reason.
And your faculties of reason don’t come back to a satisfactory level for many hours.
With moderate alcohol consumption, you can be relaxed, or “buzzed” before you get to drunkenness. But with marijuana, you can’t be “a little stoned”. That’s like being a little pregnant.
Therefore, I don’t believe the Catholic Church will ever approve of so-called “moderate” marijuana use.