I'd like to know who started that rumor. They need a good verbal lashing and their right to participate in campfire arguments revoked for at least a year.
Not all that long ago I was trying to live from paycheck to paycheck. (Police officers in the southeastern parts of the United States don't make much money.) I owned one rifle: a Ruger 77 in .223 Remington. I needed free meat and deer season was the best source. The Ruger was my deer—my everything—rifle and I never lost a deer or had one run farther than 60 yards. The bullet I used was Winchester's 64-grain Power Point.
Eventually I acquired more powerful rifles, but when it was time for my 7-year-old son to go deer hunting, an AR-15 with a collapsible stock seemed like the perfect choice. It was also chambered in .223 Rem. A Federal 60-grain Nosler Partition put his deer down on the spot. I knew the bullet would work because I'd used it in Africa on a bushbuck and a warthog.
I've also heard favorable reports from hunters using various weights of the Barnes Triple Shock bullet on deer. Though I have never shot a deer with one of these all-copper projectiles, I have used them on feral hogs. If you want to recover one of these bullets from a whitetail, you'll have to shoot him lengthwise.
On a cull hunt to test ammo on a deer farm in Missouri, several other writers and I used AR-15s in .223 Rem. to take almost two-dozen whitetails in 2 days—bucks and does weighing 100-200 pounds. No deer were lost and all the shots were not perfect. The bullet was DRT's compressed copper powder bullet.
When the Fusion 62-grain .223 Rem. load was introduced I tried it on deer and was so impressed that I started recommending it to others. Reports from the field were all positive. In fact, one farmer's daughter has used that load to take a pickup truck full of whitetails.
Last year I got to test Remington's 62-grain CoreLokt Ultra Bonded .223 Rem. load. It expands wider than any .223 caliber bullet I've ever tested and creates massive internal damage. I suggested a good friend let his 10-year-old son use this load for his first deer hunt and he put a mature doe down at about 50 yards with another AR-15.
When will a .223 Rem. not work on deer? It's like any other cartridge: If you make a bad shot, don't expect to be eating deer steaks. A .223 Rem. will work just fine for deer if you only take shots that you'd take with any other reasonable cartridge. What about BIG whitetails? It doesn't matter. A 250-pound whitetail is not twice as hard to kill as a 125-pound whitetail. Put a bullet through both lungs—let the air out of him—and you'll soon be standing by a warm gut pile.
The main misconception with the .223 Rem. is that it's just a varmint cartridge. As a point of fact, it's an excellent varmint cartridge. But, facts are facts. Load a .223 Rem. up with good bullets—any of those mentioned above—and it will work just fine on deer at any distance inside 200 yards. I've simply seen too many deer cleanly taken to have a contrary opinion.
Are there better deer cartridges than the two-two-three? I believe the answer to that question is: It depends. For a new or young hunter who might be recoil-sensitive, the .223 Rem. is quite undeniably the best choice. And the argument about needing to be an expert shot if you use a .223 Rem. on deer is unsubstantiated. If you can't reliably hit the vital zone of a deer, you need practice, not a bigger gun.
Now, if you still want to argue the point, go shoot a dozen deer in the heart or lungs with a .223 Rem. using any of the bullets mentioned and then we'll find a campfire and talk about it. Until then, you'll just be speculating or repeating the speculation of others who don't have the experience to back up their suppositions. You can't win an argument with me based on speculation.