I beg to differ.........
I've killed a couple whitetails with no problems with a .223, just most states have a 60 grain or heavier rule for bullet weight and also I wouldnt recommend using a .223 on a deer any further then 100 yards. But yes it will kill a deer, The only problem with the .223 is that it is a lower powered cartridge asfar as deer hunting goes so shot placement is vital for a clean kill so under most circustances and if you are not sure of your marksmanship then I would say dont use it.