Armed Canadian has a good screed on why gun owners need to fight licensing:
Personally, I find the idea of a license to possess a gun to be a bad idea. Solely for the prospect of abuse over time. Licensing a gun owner for the carry of a concealed weapon and licensing a gun owner for mere possession are the same thing to me. Both depend on the benevolence of the government and require absolute care in crafting such licensing rules to ensure they do not get cut off or be used to create a defacto denial of rights in the future.
The first problem with licensing is the tie to competency. Many people proposing such a scheme want owners to show they are competent. Ok, who makes the rules for competency? Who gets to evaluate them? Who has the authority to change them?
Read the whole thing.