I was in the Navy but about as far away from being a SEAL as you could get . . . fat, lazy, nuclear engineer. I've only known one SEAL in my entire life and he retired long before I was in high school (one of the UDT's that got trained/transferred to SEAL). Anyway, he's as humble, gentle, and quiet as any man I've ever met. An ordained minister who makes SEAL duty (in some VERY HOT areas) sound like it was shore duty in Pearl Harbor . . . ho hum.
Anyway, I really don't think the issue with these hardcore guys is so much caliber. .45 v. 9mm - I'm sure each man has his own personal preference but I'm pretty sure that you could give a SEAL a sharp, pointy stick and he could kill me six times before I hit the ground (probably even do it without the stick), but I'm certainly not the standard training model of the bad guy.
Never been there, never done that but if they like 9mm (or not) I'm not going to argue with them. It's good enough for me and my family of three but that's a long way from HALO jumps and foreign shores.