Alcohol is a hard drug, no doubt, and because of it's legal status many people are able to abuse it, even teens, who go binge drinking, or coma drinking, so in that perspective i'd say cannabis is better, although, cannabis isn't good either when you start too early (before 18), i started at 13 and i just know my mind would a lot less troubled if i hadn't started at such young age.So, no, weed is definatly not harmless at all, it just looks that way, but when you use it in an abusive fashion, you'll learn the negative sides, and there are a few really.
But ofcourse, as with everything, moderation is the key, i like a little shot of good whiskey when i feel tired after a hard day of work, it can calm the mood a little, i used to smoke a joint then, but i think cannabis is just way too strong nowadays, it get's me totally wasted, allmost braindead, depending on the strain, but still, way too strong.
But not everyone is the same and reacts the same, but i stopped my daily smoking and i drink very responsible (now), and never untill i'm drunk, i don't like that feeling at all.I just don't see the fun in blurred sight, vomitting and uncontrolled behaviour.