That's my point, sunray. Well, kinda. I think shot placement is the key. I know, I know, I know...but deer move sometimes and might not hit exactly what you are aiming at. That's always the response. The 223 is not suitable for all hunting situations. If you are hunting with dogs or taking 300 yard shots, then you need something bigger and heavier, but IF you are hunting a wooded area where most shots are under 100 yards, the 223 is more than capable of killing a deer DRT.
Shoot them in the neck or head or just behind the shoulder. Use a heavy bullet, and I promise the little 223 just might suprise you. It's not for everyone, but I get sick of hearing people fire off the old "223 is for coyotes" nonsense. People who spout this crap are usually the guys who A) have never used a 223 to shoot deer because they were told it was too small, or B) guys who can't shoot and wounded a deer one time that got away. There are exceptions, but they are few and far between.
I carried a 5.56mm M4 everyday for 365 days to shoot kill animals that are a hell of alot more dangerous than deer. Would I have rather had a 7.62mm? You bet! The bottom line though is that deer don't shoot back and they don't wear any form of body armor. Study the animals you hunt. Get to know their habits like your own, and then get close enough to make a sure shot. Sorry, end or rant.