This entire comment betrays an ignorance of the AR-15 and the ballistics of the common loads of its most common chambering, and as well as actual military combat doctrine.

> I’ll put the last out of the way first: theft is not a capital offense, so someone stealing your car is not a reason to shoot them.

You are absolutely correct about that. But it is absolutely reasonable to think somebody breaking into your house or car while you are in it may well have lethal intentions toward you. The courts have ruled on this more than once.

> ar15 (or any automatic rifle)

Back when revolvers were the most common handgun type, "automatic" referred to those fancy new auto-loading kind. Some hundred years later, "automatic" used in reference with a firearm means a firearm that not only self-loads after firing, but will then self-fire so long as the trigger remains depressed. The AR-15 and other rifles in the family are semi-automatic. One trigger pull, one shot. That might seem like a niggling distinction, but it's not. "(fully-)automatic" and "semi-automatic" are terms of art with regard to firearms, and have specific meanings. An automatic M-16 can fire about 600 rounds a minute and empty its magazine in about 3 seconds. A semi-automatic AR-15 can do about 60 rpm at max, and can empty its magazine in about 30 seconds, assuming the shooter can keep up that trigger speed for that long (most can't).

> No rifle has any difficulty going through dry wall or cladding, so if you’re in any urban or suburban location your odds of hitting someone else (like your family members or neighbors) is reasonably high.

This is true of any firearm, especially at indoor urban distances, But counter-intuitively, it's worse of handguns and shotguns than it is of a light rifle like the AR-15.

The AR-15 is most commonly chambered in the medium-powered .223/5.56mm round, which can be loaded in different configurations with varying trade-offs between fast & light loads (shorter bullet, more powder) and slower & heavy ones (longer bullet, less powder). A faster, lighter projectile is going to lose more of its energy upon penetrating a wall than a slower & heavier one will. The projectiles from a handgun or shotgun are much slower & heavier than the common loads of .223/5.56mm. I've read a few articles about this, which involved tests setting up simulated walls, and seeing how many walls the projectiles go through or how less far they go into a block of ballistic testing gelatin after a wall. Of all the various firearms one might chose for home defense, an AR-15 loaded with a 45 or 40 grain load is the least dangerous to those in adjacent rooms or structures.

> For rifles like ar15s you’re firing bullets that will go through whoever you hit, if you do hit them.

Just like with handgun rounds, one can buy rifle rounds loaded with bullets that expand or fragment upon impact, increasing the amount of energy they transfer to the target, and reducing the retained energy of anything that continues through the target or wall, thereby reducing the danger to others nearby.

> Given they’re automatic, you’re presumably planning on firing many rounds, which further increases the risk to others.

Anything worth shooting is worth shooting twice so it stops doing whatever it was that made it worth shooting as immediately as possible. And since an AR-15 isn't automatic, one is far less likely to do an adrenalized magazine dump that sprays bullets everywhere, and more likely to place one's follow-up shot as accurately as the first.

> Presumably part of the reason to want an automatic weapon is to manage missing the target - that’s why soldiers have them. Of course a soldier has another thing a preppier doesn’t have: all the people in one direction are valid targets.

> This isn’t the case if you’re not on a battlefield.

Automatic fire is used less on a battlefield to make up for misses and more as suppressive fire, to keep enemy heads down so your fire team or another fire team can move with less risk. When it's time to take actual shots at actual targets, semi-automatic fire is used. And soldiers on a battlefield absolutely do have to worry about potential friendlies or innocents lying in the same direction as enemies.

>Then there’s the practicality of the “protect my family” argument. For that to be useful your gun (of any kind) has to be loaded and easily accessible - which is a good way to add to the statistics of children accidentally killing themselves or others with their parents guns.

A rifle (or any gun) can be loaded and easily accessible to the one wishing to protect his family without making it readily available to any child to grab. And in all the rifle-owning households I've personally observed, the children are taught from an early age not to try get at the gun, and then quickly taught to be responsible with them as soon as they're old enough. Oh, I'm well aware of the resourcefulness and disobedience of children; I was quite that way myself. But even at single-digit ages, a child can understand the responsibility that comes with handling a firearm. In rural areas it's not uncommon to see kids with their own rifles. It's largely the kids who grow up in ignorance of firearms that can't seem to be responsible with them. And for the kids who aren't old enough to grasp that yet, it's the duty of the adult to supervise the child. An adult who can't do that isn't mature enough to have a child or a firearm.

> Finally - if you /really/ want to have a gun to “protect your family/self” use a shotgun. There’s less harm to people who aren’t directly in the line of fire, the effective distance is vastly shorter so less risk to people in other rooms, and you don’t have to be as good at aiming.

I've taken on the myth of less danger to those not in the line of fire above, but I'd like to additionally point out that at the distances one is likely going to be dealing with in a protect-your-family scenario, you still have to aim that shotgun and aiming is going to be a wash between the two. If you can't hit a target at 5 or 10 feet with a rifle, you're probably going to have an even harder time controlling the shotgun's even greater kick, and be even more dangerous to those not immediately in the line of fire than implied in your paragraphs above.

> High powered automatic rifles

An AR-15 is not a high-powered rifle. The most common .223/5.56 chambering is considered an "intermediate" power round, and is not legal for shooting even smaller deer (most common North American species have roughly the same mass range as humans). If you spend some time listening to soldiers who've been deployed, you might hear them bitching that the 5.56 round is underpowered, and it would have been better for the the US to have stuck to a rifle that used a full-size round, like the M-14. If we were talking about people keeping M-14s, or big-game rifles for home defense, I might agree with some of your points above. But the AR-15 is anything but a high-powered rifle.

Why do I harp on this? It's not because I'm a gun nut and someone was wrong on the Internet. As hackers, we (quite rightly) get pissed when we see people spouting incomplete, wrong or misleading things about technology, and then using said bogus points to advocate bad or harmful policies or ideas. It is natural and right to speak up against such false or misleading things and advocate against harmful policies. But there's a flipside to this, if we do not want others to abuse and conflate our terms of art to prevaricate or dissemble, if we do not want policy based upon irrational emotion and and half-truths to hobble our ability to work, then we should not do the same regarding other fields, and have a duty to call out our own when we see it being done.