> the tactics taken up by such a resistance would have to avoid head-on confrontations with tanks unless they have (captured) the right weapons
See, there it is where it breaks down. A light militia which gun enthusiasts imagine cannot succeed without the cooperation of the armed force. Capturing heavy weaponry needs the leap of faith that the owner of this heavy weaponry will be ready to part with it. If they are ready to do so, then you don't need your handguns and rifles because you have the mindshare. If the other side has the heavy weapons and the means to produce lots of them while denying this capability to the resistance, then your rifles won't make a difference.
Both Libya and Egypt have tribe social structures out of the cities. Those tribes have guns of their own no matter the laws. The proliferation of local militias after the government breakdown in Libya did not happen out of the blue.
The reason I mentioned Moscow in my comment is to show that people were not armed in Russia either. However, the tanks were not ready to shoot and the coup failed. Authoritarian regimes do not fail because a few people with rifles make noise in the wilderness, they fail when they run out of the conviction of their own enforcement structures that the regime must survive. The revolutions in Eastern Europe happened without a single gorilla fighter and those were some of the most policed societies in history. Have you ever asked yourself the question how did it happen?
Afghanistan is not an example of poorly armed population. Those poor fighters had Stinger missiles. Afghanistan has a porous boarder with Pakistan that allows for the movement of people, money, guns, and drugs. It is like the EU but without the human rights. What's more, the mountainous terrain makes the effectiveness of deploying heavy guns rather limited.
> Arming them doesn't mean a resistance will be successful, but disarming them would guarantee that any resistance would be a failure.
Yet, last year a big part of the executive branch of the US government tried to subvert the elections and to remain on power. Stopping it did not take mobilizing local militias. Actually, local militias were part of the problem, but their mobility was hampered in various ways, including denying them air transport. That's why I say that reality today is much more complex than waving guns around. Power and influence were exercised a few abstraction levels above that.
So, if you want to stop an authoritarian government in your country, guns are the last thing that one should invest in. Maybe one should invest just in case of some very improbable scenario, but usually, if it comes to the guns, then the fight is already lost.