I'm pretty sure that if (some) drugs were legalized it would end up reducing the amount of actual drug use overall. People in the states have way wilder house parties and problems with young people binge drinking because they can't drink until they're 21. Go to Europe and the novelty has worn off because they grew up with wine and beer at the dinner table.
Same would go for weed. The rebelliousness would be reduced, people would be less likely to smoke the entire day away, and having it controlled would make it much safer. This can't be said for all drugs though because some mess you up so much that its too much of a health risk for the user and others around them.