1: Look at the Prohobition. When it was in effect, alcohol use actually went up because it was considered cool to drink illegally. Also, crime went of because of trafficking. After they ended it, alcohol use went down because it wasn't cool to drink illegally anymore
Prohibition was a little bit different.
Alcohol is a much-deeper rooted drug in society than Cannabis is or ever will be.
Alcohol has been brewed and drunk for thousands of years.
And concerning the prohibition of alcohol, alcohol was legal and entirely unquestioned for those thousands of years before it was ever made illegal.
And when I say that alcohol is deeply rooted in society, I do mean that. Historically, it's been a favoured drink for centuries. It was for long times the most common drink, even over water, because it contained fewer diseases and infectious things.
Whereas with Cannabis, it's not had that exceedingly long period of history where it's been taken as part of perfectly-normal behaviour for humans.
Even smoking large amounts of tobacco hasn't been around for that long in comparison.
When drinking was illegal, did people stop drinking? No, they just did it illegally.
Just mentioning as above, this is because Alcohol is so tied in with Human history that to make it illegal and then have that followed by everyone and agreed upon is virtually impossible.
I don't personally think that legalising cannabis use would decrease the number of people who do take it.
I'm certain that out of all the people who do use cannabis, only a tiny percentage decide to take cannabis solely because it's illegal and that makes it edgy and cool.