I’m split roughly 50/50 on the issue.
I *like* .45 ACP and I’m old enough to recall when 9mm Luger first became a thing in US law enforcement. It got off to a bad start with a few jurisdictions insisting it be fielded with FMJ ammo under the flawed argument that if it is good enough for NATO it’s good enough for law enforcement, without understanding the key differences in roles and rules. The poor performance continued with the less than reliable hollow points available then.
On the other hand I noted shooting practical pistol competition that I could score 3 A zone hits with a 1911 in 9mm in the same it took to score just 2 A zone hits with a 1911 in .45 ACP.
I realized that the major/minor category distinctions and scoring formats generally still gave the advantage to the .45 ACP. At the same time I also realized:
1) practical pistol shooting and rules designed to promote competition were causing it to become increasingly removed from the reality of real world shoots;
2) that Jeff Cooper had become out of date;
3) modern 9mm hollow points were not giving up much at all to the .45 ACP in terms of terminal performance on assailants;
4) three wound channels in an assailant form modern 9mm hollow points had a significantly better chance of obtaining rapid incapacitation than 2 wound channels from .45 ACP hollow points fired in the same amount of time; and
5) you can carry 9 or 10 rounds per magazine with 9mm compared to 7 or 8 for the .45 ACP.
In short, it’s hard to argue against the 9mm 1911 compared to a 1911 in .45 ACP when it comes to self defense.
Either way the 1911 has a generally excellent trigger with a very short reset and it double taps faster than just about any other pistol on the planet. The 9mm Luger cartridge just takes that to full advantage.
That change over time is reflected In my current stable of 1911s
On the left side I have the .45 ACP pistols with a Kimber Gold Match II, a Charles Daly version of the Colt Commander, a Kimber Compact CDP II, and a Kimber Ultra Carry II.
The the right side, I have a Ruger SR1911 Lightweight Commander, a Kimber Pro Carry II, a Citadel Officer Model, and (with honorable mention as a sorta 1911, but one very right sized for the 9mm Luger cartridge) one of my three Star BM 9mm pistols.
Right now, nearly all my concealed carry is split between the Kimber CDP and the Pro Carry. I shoot both of them extremely well. I’m slightly faster with the 9mm Pro Carry, but the .45 ACP is still .45 ACP and still inspires a great deal of confidence when it smacks a steel plate. That confidence easily generalizes to self defense purposes.