I use to also be in the 223 is inadequate camp, but I think back to the yotes that I’ve shot with a 223 at way longer ranges than I shoot deer and at bad angles and so forth, and I just can’t look at the results I get from that and say no this isn’t adequate to kill a deer. I don’t shoot shoulders and I have never shot a deer at any angle that a 223 would not have had adequate penetration for. So all the deer I’ve ever shot I could have killed ethically with a 223.
Now with all that said I do have one counterpoint to make. If you happen to hunt in really dense heavy brush like I do, you might be making a lot of work for yourself tracking and recovering the deer. The trend I see in going smaller and smaller in caliber is that the deer still die in the same amount of time pretty much regardless of what you shoot them with, but they sure do bleed a whole lot less shooting them with small diameter bullets. I would expect little to no blood trail with a heart shot with a 223. That’s not a big deal if your hunting fields or open spaces, but it’s a huge problem in a swamp or slough. For that reason I really like 30+ caliber. Not because it kills better, it just makes finding them a whole lot easier. Really like my 358 yeti and 444!