Plus the beauty of a shotgun is you don't have to be precise. Think of the damage a standard target load of 7 1/2 or 8 shot would do to an intruder at 10-15 feet fired at the upper chest/neck/head.
I know what it would do, an aweful looking, but very much superficial and survivable wound unless the majority of the projectiles hit the neck or abdomen. Even then, an attacker has time to do whatever they feel like until their brain is deprived of oxygen, because nothing structural (bones, nervous system) has been damaged. Dick Cheney shot his buddy in the face, neck and chest at point blank range and the guy survived, and he was pretty old to start with.
People use gelaton tests to show how "deadly" birdshot is, because it can penetrate 4-6" in gelaton. That's not very objective, gelaton simulates flesh, but it doesn't simulate bones. ERs have seen numerous people shot in the chest at point blank range with birdshot, and none of the pellets penetrated to the vitals that sit a couple of inches below the skin. The pellets just kind of spread out when they hit bones, instead of smashing them like larger shot would do.
Birdshot, like a knife, will kill someone (sometimes). It's just not as likely to stop them, which is the point of an HD gun.
I don't know why people believe that there is a magic round that won't penetrate through a person or wall, but will stop them. Anything that won't go through flimsy drywall isn't likely to do much to a desperate and determined attacker.
I agree, for the most part. However, that extra 1" or so just might be the difference between an injured BG or a dead one. Yes, sometimes an inch CAN make a difference. Either way, both slugs and 00 buck are devastating rounds..needless to say.
That's why I love buckshot, because it allows me to be off center by an inch or two and still hit something crucial to stop a fight. It also won't penetrate as deeply as a single round out of a 9mm, .40, .45, .357 etc. meaning the buckshot balls will penetrate fewer layers of construction materials.
Buckshot is the perfect compromise.