Yes.
With the introduction of hemp to regular, legal agriculture, violent drug cartels would slowly yet eventually lose a lot of their income, and some would probably disappear altogether.
This isn't the only reason to legalize it, but I've come to believe that it's the most obvious one. Another one of course is that it isn't even very harmful. You can't overdose on marijuana even if you tried, because you'd just fall asleep from the lack of oxygen in your bloodstream before you reach that point. Alcohol on the other hand...
Edit:
And the reason that, to me, is absolutely the most important one is: Any substance that isn't potentially lethal in a timeframe of less than 5 years of regular consumption (and I mean very regular consumption) of that substance and that doesn't permanently or even just temporarily and noticeably alter the consumer's personality towards a violent, unstable character should NOT be illegal. Because as long as you're not harming others with what you're doing, it should be no one's but your own decision whether or not you want to do it.
These decisions should NOT be imposed on you. That's not what a government is supposed to be worrying about.
(For the reason of not harming others, smoking MJ should of course be prohibitied in confined spaces, just like regular smoking is these days.)
