My impression, from speaking to gun owners, is that in most situations in which a gun is useful you do not actually end up firing it. Your mention of "almost every situation" brought to mind the Portland mall shooting, where the shooter stopped and killed himself after seeing another man taking aim at him[1]. Other much more publicized mass shootings may have gone significantly better if the government did not publicly designate large, completely unsecured areas in which only criminals are allowed to have firearms.
[1]: http://www.kgw.com/news/Clackamas-man-armed-confronts-mall-s...