If marijuana was legalized throughout the U.S. it could be taxed and regulated by the Federal Government. Freeing up law enforcement, prisons, time, effort, tax dollars, etc. to put towards fighting the really harmful drugs like cocaine, heroin, crack.
With that said, unmoderated usage of marijuana can have negative, long-term effects. Destroying brain cells, dulling sensory perception, etc. Combined with alcohol, it can really screw up someone's senses..just think about if they were driving.
This isn't to say that the most widely accepted, and most abused drug is still to combat..the aforementioned alcohol. Right up there with caffeine and nicotine, it's a drug that everyone (and I mean everyone) embraces but doesn't (or won't) see as a big time problem worldwide.
It's used, promoted, celebrated (even idolized in some cases) throughout television, radio, cinema, music, and in every conceivable media outlet known to mankind.
I'm not here to preach temperance by any stretch of the imagination but there has been a much longer "war on drugs" with alcohol then there has been with any of the aforementioned drugs. I don't foresee anything changing in this arena though for a very long time, probably another millennia.
Just my thoughts.