You really don't. You seem like a straight-laced individual, if I told you heroin were legal in the US tomorrow would you go get some? I seriously doubt it. Anyone who wants it can already get it. Anyone not using isn't going to start due to legalization.
You know what legal thing I hear is fun but bad for you? Autoerotic asphyxiation -- but you don't see me hanging from the ceiling fan.
I urge you to research the Portuguese model, where all drugs were decriminalized to massive success [1].
[1] https://www.theguardian.com/news/2017/dec/05/portugals-radic...