Alcohol is highly regulated and manufactured, so when you look at a bottle, you know how much alcohol % is contained and you drink according to your tolerance (which is still subjective...because it drinking on an empty/full stomach can DRASTICALLY alter its effects).
MJ is not uniformly grown nor produced. It is impossible to say that 1-2 puffs will get you high, or won't, without knowing the plant, producer, etc. Again, it also depends on the person and how they react to such substances.
Some people can use asprin for pain relief; some people who take asprin will die from allergic shock. The point is...people have to know what they are drinking/smoking and if they aren't responsible, they will sin. God will hold them accountable according to their conscience, lukewarmness or carelessness.
But...for people who do research...they can safely and morally use MJ, in theory (I wouldn't know nor will I ever care to find out).
Exactly the point of the recreational use argument: it should be controlled like alcohol is, identifying strength of each variety or manufacturer, just like alcohol, so people can know what they are getting and, therefore, know how much can be used so as to relax without getting high.