So if all handgun calibers are concidered weak and not that effective in stopping the bad guy why do we (self included) spend the extra money on high performance ammo? ...
I think you answered your own question. The reason most shooters buy expensive handgun ammo is precisely because we don't necessarily trust basic FMJ Ball ammo in terms of 'stopping-power.' Look at some of the gelatin ballistic tests and make a determination concerning which one you go with (only, of course, after you are confident that your gun will reliably cycle it if you're using a semi-auto).