This is what people THINK, but in reality, what usually happens is a person makes a decision about what he/she is willing to do/wants to do/likes doing and then rationalizes the decision after the fact to help themselves (and others) believe that the right decision has been made.
So a person who carries a compact revolver for self-defense, for example, might have a lot of arguments for why 5 shots is enough and may be able to discourse at length about why it's stupid to carry a gun with more or less capacity, but in reality, those reasons probably have very little to do with why they carry a 5 shot revolver. They carry that revolver because they like the idea of/comfort of/convenience of that gun (or maybe because they don't have anything else, or that's what dad carried, or what their favorite TV character carried, etc.) and have therefore come up with a lot of arguments to help them feel good about what they do and to try to convince others understand how wise their decision was.
Similarly, a person who likes a particular high-capacity pistol and carries it in self-defense, will likely have a lot of reasons why they carry so many rounds, but in all likelihood those reasons are post-rationalization, not the real reason(s) that they chose that gun in the first place.
I'm not saying that's always the case, but it appears that it's more often the case than not.
This is part of why these debates are often heated. The arguments presented don't sway anyone because those arguments aren't really the reasons for why they carry what they carry. So the facts don't (can't) sway them because the decision wasn't based on facts in the first place--the "facts" were simply part of the post-rationalization process.
Another part of why these debates are typically heated is that most people tend to think that everyone falls into one of only three categories.
Normal people: People who take exactly the same approach to SD as you do. (Carry the same type/capacity gun with the same number of reloads.)
Nutty, paranoid people: Anyone who takes SD any farther than you do. (Carries a higher capacity gun and/or more reloads.)
Complacent Sheeple: Anyone who takes a more relaxed view of SD than you do. (Carries a lower capcity gun and/or fewer reloads.)
In reality, there's not a single right answer but nearly everyone feels like their answer has to be the only right one and any other answer must be wrong.
For what its worth, I have 3 different carry strategies involving 3 different guns, depending on whether I can wear a separate cover garment, only an untucked shirt as a carry garment, or no cover garment with my shirt tucked in. The result is 3 different round counts. It can be really confusing trying to figure out which round count is the correct one and when I'm being paranoid or complacent.
It's really more important to understand what sort of capability a given carry capacity provides than it is to try to determine an exactly correct carry round count. Knowing what sort of real-world limitations will be imposed by a given number of self-defense pistol rounds on tap can help a person develop reasonable strategies for various situations that are tailored to the number of rounds they carry.
