Shouldn't be using a long rifle with 223/308/556 caliber for home defense anyway. Should be using a shotgun, or a handgun with hollow tips. Anyone using an automatic rifle for home defense is insane.
This topic has been debated a lot. The National Rifleman's expert on home defense and tac ops recommends using an AR for home defense. Shotguns and handguns are going to have more of a risk of overpenetration than 5.56. An AR gives you more accuracy, more ammo and the ability to defeat soft body armor. Downside is you can't put them in your bedside table and they're very loud inside.