That’s part of my argument:
The impairment of the faculties is significantly higher in 1-2 puffs of MJ, than in 1-2 beers (and therefore the argument they amount to the same level of impairment is false. But that is precisely the argument some have made.
Note, however, the level of impairment is not the only cause of sinfulness (contrary to what you said above).
That's not true. Repeating yourself does not make it true.
You say you can have 1-2 glasses of wine without impairment. I am a lightweight. ½ glass and I am giggly. A full glass and I am asleep.
Our bodies metabolize chemicals through many different systems. People have different proportions and efficacy of those various metabolic systems, hence the morally acceptable dose of alcohol or MJ varies from person to person. It is that individual response that matters theologically, not whether or not that dose of alcohol or MJ affects you personally.