Do you think the alcoholic is never incarcerated? People make bad choices and have to live out those consequences all the time. Doing something ILLEGAL is a choice. My example of law enforcement costs are related to increased domestic abuse, robberies to feed addictions, auto crashes, etc. Then, once pot is legalized in every state--people will say: why not cocaine, heroin, crack--where will it end?
The 2nd Amendment gives us the right to OWN guns; not the right to use them in crimes. It certainly doesn't address drug use, so that's an invalid comparison.