Despite what Hollywood would have you believe, criminals often continue to function after being shot, often after being shot several times. "The dead man's ten seconds" is a phenomenon well and long known (the phrase comes from the Civil War). The criminal may be effectively dead from the first shot, but they still have the ability to do a great deal of harm before they're stopped. Thus, it may take multiple shots to stop them. Maybe they'll spend their entire "dead man's ten seconds" staring down at the hole in their chest." Maybe it's easy for you to bet other people's lives that that's how it will go down but maybe instead they'll use that ten seconds to hurt or kill the homeowner unless distracted by, oh, other holes being put in their body from repeat shots until they do stop.
We have repeated reports of people in military theaters shooting an individual multiple times and having them continue to fight.
And that's not even counting that robberies are often committed by more than one person. Again, local news reports suggest that the majority of home invasions involve multiple attackers.
Now, maybe in the "average" it's over after only a couple of shots. But one can drown in a stream that "averages" 6 inches deep if one happens to step in a hole that's 8' deep (the rest of the stream only being 4" or so so the "average" comes to 6"). But multiple attackers requiring multiple shots each to put down is one of the scenarios as "civilian" may face, and this without a partner, without backup on call, with just what they can grab ready to hand.
In high stress and fear situations human beings have certain common issues. One is that fine motor skills go to hell. Simply working the action of a rifle or handgun can become a thing of fumbling when one is in fear for ones life (a necessary condition of use of lethal force in all jurisdictions in the US). Much better a simple action of "aim, pull trigger, aim, pull trigger". Thus, semi-automatic.
When an attack comes, you can't be sure that everyone in your household is all together. You may, for example, have to go get the kids. This doesn't involve hunting the "bad guys." I don't recommend that at all. Get your family together and defend them if the bad guys come to you, but "get your family together" may require some moving around. Now, when you're moving around, you may have to do things like open doors or work light switches. Or maybe (it's dark, say, and this occurred after everyone was in bed) you need one hand free to hold a flashlight. Maybe you have a light mounted on your rifle but, well, you're looking for your kids. It would be good to have a light you can shine on things without pointing your gun at them, don't you think? A "pistol grip" simply makes it easier to handle and keep control of the rifle in such circumstances. Also, a more "compact" design is easier to maneuver down hallways, through doors, and the like.
The attack happens at night? When you fire the muzzle flash blooms in front of you, temporarily blinding you. Who knows what can happen in the couple of seconds it takes your eyesight to recover. A flash suppressor/hider doesn't actually suppress or hide the flash. It diverts it to the side where it interferes less with your vision allowing you to keep eyes on target allowing you to assess whether the attacker had been stopped or if you need to keep shooting, and if you do need to keep shooting you can aim rather than fire blindly (literally) and trust to luck.
A rifle is easier to aim accurately than any handgun. A centerfire rifle has more stopping power than any handgun.
Now, maybe you're not the one to hand to grab the rifle. Maybe it's your wife who's smaller than you. Or maybe you sometimes use the rifle out in the cold while wearing heavy, thick clothing and sometimes when its warmer so you don't have so much heavy clothes on. A stock that can be adjusted for length helps size the rifle for easy, comfortable, accurate shooting.
Now note what I've just described: a compact rifle with a pistol grip, "large" capacity magazine (actually "standard" capacity since that's what these rifles are designed for), flash hider, adjustable stock, and possibly a rail to which a light can be attached. While there's no "shoulder thing that goes up" (Carolyn McCarthy can never be sufficiently mocked for that) what I've just described is an "assault weapon" per the media and folk like the Brady Campaign.
It also happens to describe the best tool for defending your family against one of the between 4 and 40 thousand home invasions that occur every year.
How many of those 4 to 40 thousand families, many with children, are you willing to sacrifice?