Yes, keep the masses stoned so they won’t care about much of anything. Instant useful idiots.
While I don't care if some one wants to smoke MJ or not smoke MJ, you are right. It steals the will and some of the same people who go ballistic over second hand cigarette smoke think nothing about MJ use. The cognitive dissonance is large in this issue.
A secondary issue in medical MJ use that few take into account is since MJ is still illegal at the federal level it is an automatic dis-qualifier when trying to purchase a firearm. Voila’ back door gun control.