The best the First World can do militarily[*] is a no-fly zone, that is, grounding the dictator's main military advantage. Shipping lots of arms can only serve to escalate the war. And who knows, in whose hands those weapons would fall? Remember what happened in Afghanistan when the US was trying to root out the Soviet-sponsored regime? That succeeded marvelously and also gave birth to the Taliban.
I suspect your suggestion comes the the so-called "right to bear arms" that many in the US hold so dear. This doesn't work in all situations, but probably only in those countries or locales where you have a strong middle class. If you're poor and hungry, you tend to think of a gun not just as an instrument for self-defense and national liberation but as a tool to get the necessities you want (food, sex, etc.).
[*]Food and medical aid is probably still the best option.