Dutch drug laws and strict enforcement made sure that you can't buy any other drugs in places where you can buy marihuana. This works, and has also proven that the idea of a "gateway drug" is nonsense. When a drug dealer sells hard drugs as well, some people may be tempted, but that has nothing to do with marihuana itself.
Ironically, in The Netherlands, where marihuana use and possession isn't prosecuted, marihuana use is far lower than in the USA.