In Breaking Bad there's a scene where Walt asks his assistant how he got into the meth business since he doesn't strike him as a criminal. The assistant responds with, "Well there's crime, and then there's crime, I suppose. I'm definitely a libertarian. Consenting adults want what they want and if I'm not supplying it they will get it somewhere else. With me, they're getting exactly what they pay for. No added toxins or adulterants."
He gives a few great points, the first being, "consenting adults want what they want." Who are we to interfere? It is their body, their money, and their decision! We don't have to like it; it is none of our business. They are consensually buying and using a product, and they have that right. Locking an individual up for it is a violation of human rights. Using drugs, and even manufacturing them, is a victimless crimes; therefore not a crime at all.
The next point is, "if I'm not supplying it, they will get it somewhere else." This is a good point too since we can see that the war on drugs has not stopped people from using drugs. Historically this has never worked, and yet many still want to pretend it does. Being illegal just turn it into a black market business, and out of that comes cartels. The war on drugs is not preventing the drug trade, it is preventing a safe environment for it.
The third point is, "With me, they're getting exactly what they pay for. No added toxins or adulterants." This point is very important because, while drugs can be always dangerous, currently it is even worse. Synthetic marijuana is being sold and because it is constantly changing there are no laws against it. People buy it, knowingly or even unknowingly, and end up very ill or paralyzed. The dealer will not be held accountable due to this all being under the table. Legalized, actual dispensaries could open up and would have standards to meet. Not because of regulation but because they would go out of business fast if their products were fake or sub-par. Free markets will ensure that reliable products are available.
The last (and best!) point is obviously that he is a libertarian. What isn't great about that? He makes meth, but he is not hurting anyone, drugging anyone, or violating any human rights. He is simply supplying the market with a product it demands. He knows he is not a criminal, and we should too.