There are people who thought and still think alcohol isn't harmful either. I know a lot of them and most who drink every night more than, say, just one glass of red wine at dinner have drinking problems and some don't even know it.If you can't have fun without getting buzzed...not a good thing. by the way, when I talk about "most" I am only discussing the folks I know. Maybe somewhere people can get buzzed or drunk every night and NOT have alcohol issues. But amongst my group of people I know, they get into serious situations even when just buzzed, such as hitting on a friend's husband, speaking inappropriately in front of a child, the beat goes on. Pot doesn't do that, but it has it's own problems.
Pot, in my guesstimate, will turn out to be just as bad as alcohol for the body of anyone who abuses it and, like alcohol, for the percentage who can't tolerate it at all without becoming mentally ill from it. It's a fact that pot causes depersonalization/derealization and though most of you never heard of either, it is one of the most horrific feelins on earth...like you are not a real person and the world is a dream. I can't explain it better than that, but it was, of every symptom I've ever had, the absolute worst one I ever felt. I was fortunate it went away. In many, it doesn't. Often pot is the trigger for this horror. I have also read that it can trigger latent, underlying schizophrenia. And wait until they find out what pot smoke does to the lungs...probably a lot like tobacco smoke.
I do think, if you are able to tolerate pot, and take it only recreationally it can be harmless, as long as it's not loaded with other drugs.
But for those who will be intolerant of it, it will not be harmless, just like alcohol isn't harmless to so many alcoholics.