I'd assume Colorado is one of the more pro-gun states.
It used to be. But when the issue of gun control boils down to keeping nutcases and criminals from getting firearms, Colorado is likely close to the national average. Deer rifles for hunting has little opposition. Guns for a nut intent on a massacre or in the possession of urban street gangs to terrorize the poorer parts of town is another matter.
Why shouldn't guns be licensed? Automobiles are similarly deadly, and most states have drivers' licensing tests. Shouldn't people know enough to not cross a solid double line, that a red light means stop, that speed laws exist to make highway use safe, and that drunk driving is not only illegal but dangerous? Shouldn't people have to prove suitability for owning a firearm?
I have never owned or used a firearm, but I figure that I could pass a concealed-carry licensing exam easily. At that I know that certain firearms are illegal, that one must assume that all guns are loaded, and that pointing a gun at someone is
prima facie assault with a deadly weapon. I also recognize that alcohol and firearms are a dangerous combination.