There's a lot of ignorance in this thread about the situation in Colorado. The medical marijuana boom has not abated one bit and it won't by the time this law goes into affect. There are dispensaries everywhere... in some places as common as liquor stores, and there seems to be at least one in just about every town. Every one of these can transition from a medical marijuana dispensary to a legal regulated marijuana shop with ease. Some business owners may be more cautious about this than others, but the man power and resources the Feds would need to shut down every one of these would make such an endeavor ridiculous (which is not to say that the Feds are not ridiculous enough to try it).
The dispensaries have already completely changed the marijuana market in the state. The dispensaries and home growers are the source of just about all the pot on the market, whether used by people with medical cards or not. This hasn't caused any influx in crime from the former sellers looking to get into a new game. The transition from medical dispensaries to legal shops will have no tangible affect on this. The notion that it'll increase crime as an argument against is an obtuse reach at best.
Frankly it's a bit silly to cling onto the ruse that it is being distributed for medical purposes only when so many people with cards have flimsy justifications for having one. Just legalize it and do away with the ruse. And if you are against that, be consistent and argue for the prohibition of alcohol and tobacco. That one is legal and the other isn't is completely arbitrary.