It will give the US the political will to settle alot of issues created because of the current state of the Mexican border which will branch into many things. Crime and Punishment, immigration etc etc.
Cartels eventually messing with the US in force is a matter of time and is better if is sooner rather than later.
Cartels are in business to sell drugs and weapons. They do not gratuitously target those who pose no threat to them or when doing so could harm their own business. As long as they are still profiting from their own product sales, cartels do not pose a threat to the somewhat comparatively small business of Colorado pot shops.