Most defensive shooting "experts" spend a lot of time touting the particular caliber and handgun type they believe is the answer to all personal-defense issues. Unfortunately, a study of defensive shootings will soon reveal that every caliber and every action style has had its share of failures along with its successes.
Additional studies of violent encounters indicate the presence of just any defensive handgun and the willingness to use it, if necessary, is the major factor in successfully stopping criminal attacks. For the most part, criminals are cowards who will retreat if they see their intended victim has half a chance of effectively resisting. Bad guys don't like the idea of a level playing field.
The first rule of surviving a potential gunfight is having a gun—any gun. The old timer who grabs his .22 LR rifle to repel boarders has just taken a giant step toward winning. The woman who gets the .32 Colt semi-automatic that once belonged to her daddy out of the nightstand has just increased her chances of surviving a thousand-fold. Bad guys don't like to deal with people who fight back.
So, here is a pretty good recipe for personal defense: You should carry the most powerful handgun you can shoot and conceal well. If that is a .45 ACP, you are in good shape. If it is just a .22 LR revolver, you are far better off than if you had to throw rocks. When one is willing to get professional training and actually practice what he has been taught, the defensive handgun selection may change. That is all to the good. Bad guys don't like victims who can shoot well.
Personal defense is like everything else in life. We can spend time wishing things were different or we can work with what we've got. Don't follow the fads, just use enough gun.