As someone who spends most of his time working for and with wealthy and successful people (and therefore going to their parties because that's where things get done).... almost all of them smoke weed, and a fair amount of them are doing harder drugs. Here's who else smoked weed: The last three Presidents, at least.
I'm sorry, but the world you are coming from is a bubble that doesn't really exist. In the real world, drug use isn't just pervasive; it's downright common. On top of all of that, alcohol is sooooooo much worse a drug than marijuana that it's absolutely ridiculous. It's chemically addictive, extremely powerful, and inhibits decision making... yet the majority of the population manages to use it reasonably in moderation.