"He who would succumb to the irresistible power of necessity must suffer what fate destiny decrees"
In other words, why do you wear shoes? You don't necessarily need them, after all you might not cross harmful terrain. You wear them, precisely, because you might encounter terrain that would harm your feet without protection. Now, extrapolate, going from a instance of lesser importance (shoes for foot protection) to one of greater (modern means of self defense for life protection).
Shoes are worn in reasonable anticipation of harmful terrain, so should modern means of self defense be word in anticipation of aggressive and harmful people. Not wearing shoes will, in most cases (as regards working people), result in only lacerated feet. Most of these feet will heal (no pun) in time, but some of these wounds will become necrotic or otherwise infected. Now, in this case, the choice not to protect ones feet might result in the loss of them or even life.
Modern means of self defense are carried in reasonable expectation of harmful situations. Not carrying such means, in most cases (as regards all people), will result in nothing; but sometimes, when a situation such as the aforementioned occurs, not having such means will result in the loss of life. Since it is impossible to know when these situations arise it is an injustice to be deprived of the ability to confront them in a manner most favorable to success... that is armed.
It is funny you bring up an 'anarchist argument' and then continue to talk about the second amendment. If you can't see why, I am sure a person more versed than I in the eccentricities (unconventionalities) of proper anarchism will explain it to you.