A solid 9mm, like a Beretta 92FS, Sig, or Ruger P95 is 1) very reliable 2) very accurate 3) has significantly less recoil, and thus easier to handle than a .45. In addition, the higher capacity magazine on a 9mm (which in some of the earlier pre-Klinton ban models you can still get with 15-16 rounds) is another plus, given that criminals often travel in packs.
So to all you ex-Navy Seal and Spec Ops types thumping your chests out there, my hat's off to you. But when it comes to the defensive needs of the average civilian (a topic which, if you claim to be a Second Amendment defender, you should NOT be sneering at) the 9mm in most cases is the tool of choice.
The real advantage of a 1911 is the simple, reliable design. The .45acp simply outperforms smaller rounds as well and before a silly communist in the White House agreed with the UN to start destroying armories full of durable and proven military small arms in .45acp and 30/'06, we had millions of militia weapons available to a citizen militia in the event of the kind of emergency we now face, all of which were easily rebuilt and used two standard and proven military cartridges.