I've heard lots of people have used .223s to deer hunt,a lot of States allow it,unfortunately here in Indiana it has to fire at least a .243 bullet but shoot it's been used a long time in the military and people are bigger than deer . Good going there by the way .
I use my 223 Wylde for deer all the time. And pigs. I use the 65 grain Sierra Game King. Put it in the boiler room and dead deer every time. It's also good on pigs. They just seem to fold up when hit in the boiler room with it. Of course I have never shot a pig more than a few yards (feet) with it. I think pigs succumb to hydrostatic shock more than deer.
I'm not a fan of 223 for hunting. I personally like my hunting guns the way I like my women...
"A little too much, is better than a little too little!"
Of course common sense should be used. I wouldn't use a .338 for deer or a 300 Mag for coyote. But some do. To each their own. The most important thing is the hunter, not the gun, and you seem to have that part covered.
I've killed several deer with a 223 but I'd be the last to tell you that it is a "good" deer cartridge. It just isn't. Anything but a very good shot can, and probably will, result in a long death run and possible loss of the animal. If it's all one has to hunt with, that is one thing. If it's a "caliber of choice", that's another. A 243 Win is about the minimum I would say is a satisfactory deer round.