I also carry a .45. I chose it because of real world observation, academic research, and a hefty dose of personal preference. Primarily because from my investigations I've noted that slower/heavier rounds penetrate intermediate barriers better, deflect less, and cause more damage on the other side of car doors, windshields, etc whereas faster/lighter fragment earlier, causing less damage. Given my role as a police officer, I'm more likely to have to engage someone through an intermediate barrier, hence the heavier caliber.
This is exactly what sold me on a .45, and actually the exact reasoning that my cousin (the police officer) gave me.
He had said, "It won't do a through and through like a 9mm will." I assume (correct me if I'm wrong) that means going through a person as easy as a 9mm.
When people criticize my .45 1911, I take it with a 230 grain of salt.