It's not hypocrisy at all.
Alcohol is a legal stimulant, of which the side effects and consequences are very, very well known.
The same can be said for that other legal stimulant, nicotine.
Weed, dope etc is another matter. Whilst extensive research has been carried out, the side effects and consequences are not yet fully understood. It is an illegal substance for good reason and whilst that may or may not change in the future, in the here and now, it's an illegal substance.
For me, there are two issues - the first is that stimulants (of any flavour) have no place on the flightdeck. That's why there are limitations on alcohol consumption before duty.
The second is the attitude towards drug taking. OK, let's play devil's advocate. You say, hell, it's OK - the odd joint hurt wont hurt (despite the great unknown consequences). You're then raising the barrier. Somebody sniffs the odd line of powder. Do you draw the line there?