There is an absolute philosophic interconnection between the right to life, the right to defend life, or the right of self-defense, and the right to the means necessary to defend life from any and all that would contravene that right and act to deprive the innocent of life.
The philosophic position is simple to follow. It really is simplicity itself.
If one posits or accepts the proposition that life itself comes ultimately from the hand of Almighty God, one necessarily can see that the right to life is from God Himself, and does not come from any created entity, whether that be the state, the government, the family, a corporation, or anything else.
Consequently, in a philosophic sense, one cannot illegitimately be deprived of that right and must be capable of resisting any and all who would so deprive one. In other words, one must have access to the means necessary to prevent such deprivation.
This is where guns come in. Guns afford even the weak the opportunity of resisting the predatory activities of an unjust aggressor.
A corollary here: The position of those who posit a right to life, and defend such right from the imprecations of those favoring abortion or euthanasia, but then refuse to recognize and support an individual right to keep and bear arms is not tenable.
One really can not indicate a belief in the right to life and then subvert the right to the means necessary to defend life.
To be blunt: One can not be pro-life and anti-gun without being an absolute hypocrite.