I moved stuff around so I can address related points together.
No, I do not agree that if guns used in self defense are likely to be used wrongfully, then it would follow that there would be more cases of accidental injury than cases of successful self-defense. That doesn't follow at all.
This would assume that every time someone uses a gun, or more, that someone would get hurt. That is obviously not the case.
The point is that MORE people than otherwise will be hurt because MORE people than otherwise are utilizing guns.
Here's an analogy since I know you love mine
Say a bar owner knows that when there are 50 people in his bar, it is probable that at least 2 of them will get into a fight. But he also knows that when that number jumps up to 75 people, at least 6 people will begin to fight. The ratio of fighters to non-fighters is small, but increasing the number of people exponentially increases the number of fighters. The same with guns in self defense and guns in wrongful accidents ratio.
And yes, questioning whether guns were a necessary or exacerbating component in the self-defense is exceedingly relevant. Because you could claim that since 10 people were saved by guns via self-defense, we should then ignore the 2 people who get shot. But if guns were not necessary, or in fact caused the problem in the first place, then the trade-off of 2 lives for the 10 suddenly doesn't seem like a good trade after all.