I agree an AR can be used as a home defense platform, but it can also shoot through walls, most any round can. The caliber used, the type of round, steel, lead, hollow point etc matters as does the wall type. Most American homes are not built to stop any type of rounds and most people defending their homes would aim at their intended targets, I have never seen any reports of people being injured by a neighbor fighting off home invaders, but innocents being hit by drive bys, and other types of shooting are not uncommon.
I keep a pistol bedside to defend my home, a rifle would be overkill and I have zero neighbors to worry about. In the end, it all comes down to training, having a plan and working through the plan. If neighbors close by could be injured the plan should reflect that and work around it. Hope that helps.