Evil and good are moral terms that apply to entities that can make choices. A gun is a non-volitional object. Guns have no power of choice.
Unlike a gun, the user of a firearm possesses free-will and can be judged for their actions. It is only the user of a gun who is good or evil: a woman who uses a gun to shoot a man wishing to rape her is acting selfishly to save her life; a bank robber using a gun to rob a bank is acting irrationally and self-destructively.
To say that a gun is intrinsically evil because criminals — and corrupt governments — use weapons to rob peaceful citizens, is like saying water is evil because people can drown in it.
The right to own a firearm is an application of the right to self-defense, i.e., the right to obtain the means to defend oneself. The right to self-defense is itself is a corollary of the right to life (a corollary is an implication of a principle). It would be absurd to say one has the right to life in theory but does not have the right to the means necessary to protect that life. It would be like saying one has the right to life, but not the right to purchase food. This is what opponents to the right to own a gun for self-defense are really against the right to life and the means to defend it.