Well, it may not be "immoral" in the sense that you are thinking. Buddhism is a means towards liberation. We practice morality towards that end - not to avoid some sort of divine punishment.
Buddhist morality is called "Sila." It can mean ethics, virtue, morality, precepts, and can even be translated as "habit." It is skillful behavior (good habits) that lead us away from craving/thirst/attachment and towards liberation. One part of the eightfold path is right action,
which calls for 5 precepts
1. I undertake the precept to refrain from destroying living creatures.
2. I undertake the precept to refrain from taking that which is not given.
3. I undertake the precept to refrain from sexual misconduct.
4. I undertake the precept to refrain from incorrect speech.
5. I undertake the precept to refrain from intoxicating drinks and drugs which lead to carelessness.
The last of these is not a moral precept in the sense that it is necessarily wrong doing - but it can and does lead to carelessness, which might involve breaking one of the other precepts. It also will make it impossible to practice Right Mindfulness
, and I certainly don't see a stoned person ever attaining any state of Right Concentration
. I could keep going on this theme!
Another interpretation is that it's not so much about rigid morality but actions that take us away from clarity. I know some that take the 5th precept even further and refrain from anything that can muddle or rattle the mind including certain types of "intoxicating" media, television, etc.. I think of the 5th as having a mind that can think clearly.