I am sure that, in any given situation when faced with a gun pointing at me, I would like to have a gun pointing back.
However, this is not the basis of an ideology; it is merely a statement of self-interest and perhaps common-sense.
Libertarianism purports to be an ideology; people claim to be libertarians; they promote libertarian values and principles; and they formulate and implement libertarian policies.
American and some British libertarians oppose gun control and argue that you and they have a fundamental right to "bear arms".
Their usual argument for doing so is that you and they should have the right to an armed defence: if one outlaws guns only the outlaws will have guns.
But this libertarian position has a stark implication which they will always seek to evade and avoid.
Anyone can point a gun at you; but only the libertarian believes that the person pointing that gun at you has a fundamental right to possess it.
I will admit that I would want, in my self-interest, a gun when faced with a gun; but libertarianism - as an ism - demands more than this; and I for one will never concede that the person already with the gun has a 'fundamental' right to bear that arm.