Yes a .223 will kill a deer. It happens to be legal to use one on deer here in Texas.Is it a good choice for deer? NO! There are probably 20 cartridges, with not much more recoil than the .22's that are better choices for deer hunting!
If its legal where you hunt and you are good enough with it, then thats your business! But, even if its your cartridge of choice, you shouldn't be recomending it to others!