There isn't really a conclusion, just uncertainty. I do not know if Marijuana constitutes a grave threat to our society or not. If it does, it will likely be indirectly through it's effects as a gateway drug or by inducing indolence. There is a chance that nothing of great consequence will happen.
About Crack and Meth i'm pretty sure. Allow that stuff and things will go for us much the way they went for China with Opium.
The problem is, they cannot be separated in terms of Libertarian philosophy. If people have a right to smoke pot, they also have a right to smoke meth or crack or heroin.
They will even have a right to smoke the latest Pharmaceutical slave maker, no doubt some sort of a derivative of Rohipnol or something.
Open the door to the legal manufacture of designer control drugs, and we will see something really significant. Open that door, and that is what will be coming through eventually.