Ah i assumed of course it would be weed after the last dive of the day, if it was before a dive, then I agree with both of you guys: this would be totally irresponsible.The issue with marijuana on a boat has the implication that someone is likely to be impaired. We, as divers generally have a rule of thumb that the first alcohol of the day means diving is done for the day - the same rule should be in place for weed. I certainly would prefer not to be buddied with someone who is buzzed.
BTW I tend to agree on the decriminalising bit - Canada have just done it and it doesn't seem to have had any major issues.