It's really a tough call. I do NOT think it should be banned, but rather treated the same way as alcohol (at least in sports). Alcohol is worse than marijuana when it comes to health and fitness, in my experience (as a former athlete and coach). Both in moderation wouldn't hurt.
Re: the Colorado and Washington complications .. Well, it's "illegal" for people under the age of 21 to purchase and consume alcohol in all 50 states. Yet alcohol is not a banned substance in the NCAA.
I think changes do need to be made, and they will happen in due time, as the nation watches the happenings in Colorado and Washington re: marijuana.