Educate the person you are responding to by providing information about why the military chose the .223 round. The reason for the choice was not its killing power, but rather its wounding power. This way, the enemy could be easily injured, putting a strain on their resources, without having to be killed.
also the military did not chose the .223 round because of its killing power that's what the .308 is for. the .223 was chosen because of its "wounding" not "killing" power. easy to shoot your enemy in the leg and have his comrades rescue him and waste precious survival resources trying to heal him. do some damn research man.