A threat who isn't a "highly trained" person is likely to see a homeowner with an "M-16" (that IS what the perp is going to think it is) and decide either A) oh s--t, feets don't fail me now, or B) oh s--t, "PLEEEEEEEEEAASE DON'T SHOOT ME, PLEASE GOD NO!" and comply with your orders while emptying his bowels.
Still, there is always Mr. Murphy and the idiot who decides he can take you out fast-draw with the .25ACP tucked in his pants. If you are going to defend your house with a gun, you have to accept that you might have to kill somebody some day. You really don't want to, but it's a possibility you must accept. If you want to be "non-lethal," get rid of the AR and get a rubber-padded baseball bat.
Personally, the only "home defense" scenarios I can envision utilizing my AR15 for are Watts-style riots, total breakdown of civilization, or defending my property from jackbooted thugs. For everything else a Glock or a 12ga will do the job and make the prosecutor's attempts to pin "rambo wannabe" on that much harder.