I have no problem with a .223 for deer if one uses a bullet which can reach the vitals. Most bullets loaded in a .22 caliber cartridges are designed to explode. This is not ideal for hunting deer. If the bullet will reach the vitals then knock yourself out. If not then the gun is unsuitable, whether we are talking a .223, .22-.250, .243, .25 06, .270, .30 06, .300 win mag or any cannon one wants to shoot. I think we worry too much about caliber and not enough about what we are hitting them with. The thunder makes the noise but the lightning does the work. Hit the deer with something which can do the work and ya eat venison.
Dr Fatguy