Sorry Guys!! Didn't know there were nerves so close to the surface on this issue. Kinda feel like Zumbo. Of course a 223 will cleanly kill a deer. A .410 will cleanly kill a goose too. Might even be legal too. Doesn't make it a good idea. Why use a caliber thats recognized by State wildlife agencies as minimally acceptable (in those state where legal) when there are so many other better choices?
In perfect world where a competent, experienced and relaxed hunter, shooting from a solid rest at unalert broadside deer at close range using a stoutly constructed bullet from an accurate rifle sighted in for that bullet and hitting a relatively soft tissue and vital organs (phew!), a 223 will most likely work almost every time.
In the real world the novice hunter will be shooting off a so-so rest (if any) at a kinda broadside nervous deer shooting inexpensive FMJ's or economy varmint bullets (Dang, those Barnes & Partitions are expensive), hit the shoulder and if he or she is real lucky will get a chance for a follow up kill shot and recover the deer in time to save the meat.
Watching a deer stumble around in the sagebrush with a festering baseball sized crater in it's shoulder aint fun and it aint pretty. I've got too much respect for the animal and for the sport to risk it.
I'm thinking Elmer Keith was on to something..."Use Enough Gun". Guessing Zumbo would agree too.