Our government has a responsibility to protect us from harm. In fact, some would argue it is the federal government's only real responsibility and function. Ingesting smoke into your lungs, no matter what kind, is not healthy for you. In my opinion, it would go against the foundational responsibility of government to legalize something known to be hazardous to your health. Save your arguments about how pot is beneficial to some, it is the delivery system which poses a problem. Any time you ingest smoke into your lungs, you are ingesting carcinogens, and putting your respiratory health at risk.
I'm not saying we should make things illegal that are bad for your health, but we shouldn't compound the problem by adding to it. If we knew then what we know now about cigarettes, it would have been wrong to legalize them as a commercial product. It is the only product sold, that if used as directed, will kill you.
Decriminalization would eliminate the onerous laws currently plaguing the pot smoker. It would free up space in our prisons, as well as resources for law enforcement, to go after much more serious drug problems. I would even be willing to accept a "medical marijuana" exemption, where doctors could prescribe it as a controlled pharmaceutical for certain patients. I just feel that complete legalization, having it sitting there on the store shelf along side cigarettes, and taxing it, is the wrong way to go.
(I am an occasional pot smoker)