That "self preservation can't ever be considered undesirable" is true; I'd never argue otherwise. It is built into the nature of all living creatures. Even a mosquito will bite where not not seen to avoid being 'offed'.
But, even self preservation is not unlimited as proved by the Sandy Hook educators who stood in front of the killer to defend their kids.
The earliest constitutional Americans were concerned about defending the nation from the then known standing armies of foreign countries. We no longer need militias to do that. If an argument is to be made for the need to defend against our standing army, my counter argument would be to abolish our armies instead and indeed return to militias.
It seems to me that, in an argument for self-defense, a logical starting point would be to reduce the dangers against which we need to defend, rather than accepting an arms race between Americans on the two sides of our politically divided nation.
Well armed, poorly-regulated militia patriot types (for whom military style weapons are most popular) scare me, but I am not going to arm myself when all life is uncertain. I am as likely to die, struck by a bus as I cross the street with my purchase after exiting the gun store, as I am to be a home invasion victim.
My philosophy: there is no difference between you and me (no differences among all of us) and thus no reason for fear.
My personal philosophy is a difficult road to walk when I choose to not kill even the mosquito.
All differences are superficial. Stripped of all of the accidental (temporary or could be otherwise) differences like gender, race, nationality, education, interests, experiences, hopes, fears, etc., we are left with the unity of existent awareness. We are conscious beings. Our existential awareness is the ground upon which all identity rests and is constant regardless of changes in thought. Awareness is, as though, the unified field of all physics. No mind, no knowledge. Even thoughtful scientific, materialist research about a world devoid of conscious awareness requires the existence of that awareness.
I am willing to stand in front of the 2nd amendment to defend my kids' future.