Now, that's not likely to happen, i.e. ideally you can follow Rule 4 by changing your angle, but ... well, in the real world your alternative just isn't going to happen. Unless they take personal responsibility (and in anti-gun places like NYC that's very hard since there aren't many places to shoot), most police aren't good shots, don't have to shoot very often, and aren't well trained. At the Connecticut legislative hearing on this, the anti-gun police officer giving testimony had to admit training was on the order of a few hours a year. And then there's fire discipline, you have seen the picture of the pickup truck, wrong model, color and with two Hispanic ladies delivering papers, that was perforated by LAPD cops who were ... concerned that one of the own was hunting them?
However, that's not the main reason for using expanding ammo in self-defense. We, civilians and the police, are not allowed to kill per se, nor is that our objective. If in such a situation, we desperately want to stop someone, and for handguns "stopping power" scales with the diameter of the bullet, including expansion if that occurs, lethality with the number of holes you punch in someone.
For .223/5.56 NATO, Full Metal Jacket (FMJ) rounds have very iffy stopping power (details on request), so using them in self-defense if you have an alternative is a very bad idea.
I figure innocent bystanders who get shot are hit by fewer bullets than the people who are actually being aimed at. Pulling numbers out of my ass, say innocent bystanders that are hit are hit by 1 bullet on average, and crims that are hit are hit by 3 bullets on average.
The questions to me then become:
1) how many innocent bystanders are being killed by those single bullets, and how would that number change if they were FMJ instead?
2) Given the average number of times crims who are shot at are hit, how likely is it that they would still be killed if the police were using FMJ?
I suspect these two factors work out such that FMJ would be slightly more dangerous to police, but vastly safer for the general public despite the increased penetration power. Police are signing up for it, so I am okay with putting them in more danger to keep the public safer; I am sure police unions would throw a fit over that though.
(I think it would also be revealing to examine if perhaps the lower penetration power of fragmenting rounds make police have a more relaxed attitude towards accuracy.)
The raw facts I've just outlined don't disprove your thesis, but as I understand it the details do. It's also the fact that outside of situations where politics are in play, expanding bullets are the universal choice, all things considered.
Note this includes civilians who carry, there's 7.5 to 8 million as independently estimated last summer by scholar Clayton Cramer and the GAO respectively, plus those who can carry concealed without a license in the handful of states that allow that (Vermont, Alaska, Arizona and Wyoming). Unlike the police, we don't have legal or political protection from accidents, we own every bullet we fire, and a loved one could easily be one of those too close bystanders (or on the other side of a wall or the house, whatever).
Maybe we're wrong, but using hollow point ammo is what almost all of us have decided to do.
First of all, accurately firing a weapon requires one to relax, breathe slowly, reduce the heart rate, hold still and concentrate. Almost all situations that justify shooting at people involve imminent danger of death to the shooter, the shooter's allies or innocent bystanders. That pressure produces a physical response exactly the opposite of what's required to shoot accurately. Good training can partially compensate, but it's impossible to replicate the psychological and physiological effects of the possibility of imminent death without a significant risk of actual imminent death.
Secondly, non-expanding ammunition will easily penetrate through a person and retain enough power to kill a second person. In most cases, a single bullet could kill three or four people if they were properly aligned. Ideally, the shooter will try to make sure the bullet will stop safely after penetrating the target, but circumstances that require shooting people are rarely ideal. Using bullets that are easier to stop is better for bystanders.
Finally, bullets do a surprisingly bad job of instantly physically incapacitating people. There are a number of cases on record of violent criminals continuing their attempts to murder police officers after being shot multiple times, even after receiving wounds that aren't survivable even with immediate medical treatment. Most people stop fighting when shot for psychological, not physiological reasons; they didn't like being shot and don't want it to happen again, the pain is too severe to continue resisting or they hope that giving up will lead to medical treatment and a better chance of survival. Barring that, there are three ways a bullet can incapacitate a person: damage the brain or spinal cord enough to prevent movement, cause enough blood loss that the brain shuts down, or damage the heart enough that it can't pump blood to the brain. Expanding bullets have a higher probability of causing these effects than non-expanding bullets.
I think it is definitely worth considering if reliance on expanding rounds that are not perceived to penetrate has an effect on the tendency to take risks in situations where there are people behind the target. As I see it, considering the number of shots often fired by police and their poor accuracy, it doesn't really matter that the rounds won't go through multiple people. The more accurate police are, the more fragmenting rounds start to seem sensible to me.
Being concerned about bullets going through badguys and hitting innocents or hitting multiple innocents in a row instead of just one seems like... premature optimization.
From Wikipedia on the FBI shootout, matching my memory of various accounts:
"As Platt climbed out of the passenger side car window, one of Dove's 9 mm rounds hit his right upper arm and went on to penetrate his chest, stopping an inch away from his heart. The autopsy found Platt’s right lung was collapsed and his chest cavity contained 1.3 liters of blood, suggesting damage to the main blood vessels of the right lung. Of his many gunshot wounds, this first was the primary injury responsible for Platt’s eventual death."
He was functional for quite some time after that, including killing the two agents who died in the shootout. Here's some illuminating details from the end of that section:
"[...] The bullet penetrated Platt's chest and bruised the spinal cord, ending the gunfight.
The shootout involved ten people: two suspects and eight FBI agents. Of the ten, only one, Special Agent Manauzzi, did not fire any shots (firearm thrown from car in initial collision), while only one, Special Agent Risner, was able to emerge from the battle without a wound. The incident lasted under five minutes yet approximately 145 shots were exchanged.
Toxicology tests showed that the abilities of Platt and Matix to fight through multiple traumatic gunshot wounds and continue to battle and attempt to escape were not achieved through any chemical means. Both of their bodies were drug-free at the time of their deaths."
Yikes. And there are more incidents like this one.
That has always really bothered me. I get the point for hunting, having the animal die as fast as possible is good, but I don't buy the argument that they are important for police because they have less penetration power. If we want to reduce the number of people accidentally shot by police, I think we would be better served by training police to actually hit what they shoot at, not giving them bullets that hopefully won't go through as many walls or people.