Most people who live an otherwise decent life, are going to panic to one degree or another when confronted with a life or death situation. Fine motor skills that got you bull's eyes at the target range are gone. Now, you are going to hope that you even hit your target, let alone get a three shot group the size of someone's heart.
If all you're probably going to get is a hit in the bad guy's arm, or a glancing rib shot - wouldn't you want the biggest hole there as possible?
Go with a .45!
A Highly Trained, Professional Idiot