CathInfo.com

3) Mark79 is looking at the issue from the vantage of medicinal benefit, and in that regard he seems to have some knowledge.  But from the moral perspective, I’m sure he would not presume to know more about morals that traditional priests.  But in any case, the article is not discussing medicinal use.

With all due respect to priests everywhere, isn't there a limit of "full understanding" that can be reached by laymen and priests alike?
Let me put it another way: it doesn't take 6 years in the seminary and the Priestly character to understand "losing the faculty of reason on purpose is a mortal sin".

Just like it doesn't take a PhD to understand that seeing buildings or ships dozens "too far away" (farther away than should be possible) based on curvature-of-earth calculations poses problems for the Globe Earth model. Some things are common sense. Those without certifications (seminary training, PhD, college degrees) are not therefore STUPID and unable to grasp basic concepts!

Put that together with a deeper knowledge of state-of-the-art in marijuana production, latest scientific research, and medicinal properties of the various chemicals in this herb, and some (like me) are led to conclude that an article by Mark79 is worth much more, holds more weight, commands more respect, etc. than a similar-length article by the likes of Fr. Scott.

In other words, the moral component is basic and therefore EASILY grasped by the untrained layman: "purposely taking away faculty of reason in human being = grave sin".  Mark79 could easily "catch up to" Fr. Scott's grasp of that. Now what? Mark79 has then proceeded to fly loops around Fr. Scott with his up-to-date, educated, and nuanced knowledge on the issue of medicinal pot use.

Sean, please define "recreational".  This is key to a rational debate. 

Any non-medicinal use.

PS: Even some medicinal uses are prohibited (eg., when there is no necessity, and/or cases in which the benefit does not outweigh the risk to health, etc).

It is false to contend that “morality hinges entirely upon the impairment of the faculties...”

Am I morally permitted to drink poison (or otherwise harm myself) if there is no impairment of reason?

For example, if it were shown that sustained use of MJ in small doses (microdosing) causes schizophrenia, would it still be a morally licit practice?

Alcohol is technically a form of poison, as are, broadly-speaking, most modern medicines (chemo being an obvious one); so yes, you could take certain poisons if the end of the action is still good. You could even take microdoses of cyanide (under strict medical observation) to increase your resistance to it.

Now, if your aim in drinking poison is to cause significant harm or impairment to yourself (again, the same principles surrounding alcohol consumption), then no, it is not morally licit. Which is literally what Lad, and others, have been arguing about MJ. Which in itself has been outright condemned by some as inherently evil.