When there is a tyrannical government in power who is violently oppressing the people, would any new laws eventually prevent me from walking up to an agent of the tyrannical state and shoot them in the head? i.e., would it be possible to have localized insurrections against government? Make no mistake, it is this fear that prevents most governments from overreaching.

If the answer is no, then the rule is not allowed. Licensing would be a slippery slope into complete gun control and consolidating power over the people.

If you want further proof, look at what is happening in the socialist countries in South America. The government is murdering their own people who are defenseless.

If you want further proof that an armed populace is a good check against (real or perceived) tyranny, look at Afghanistan, Iraq, and of course USA (hello UK!)