King James Version of Matthew 19:18
(here JESUS is listing the 10 basic commandments for the rich man who would like to know what else he can do to merit eternal life)
"...thou shalt do no murder, thou shalt not commit adultery..."
Joseph Smith's Version
"Thou shalt not kill, thou shalt not commit adultery..."
The only modification to the summary of commandments given at Sinai is a stipulation that we should not kill anyone for any reason. The Old Testament has the correct list, but some fool tried to slip one past us possibly to appease a rich person they knew who had killed someone.
The people of Ammon (the anit-Nephi-Lehis) who allowed themselves to be killed rather than fight against their ethnic brethren the Laminates are certainly the celestial standard of this law. JESUS allowing himself to be killed when he could have easily prevented it, is the conclusive piece of evidence. If we want to live where GOD lives, we need to follow GOD's example. I would hate to be the guy saying "OK, JESUS I know you sacrificed your perfect life for all of us, but that guy who stole my lawnmower had to go."
My guess is that the terrestrial standard is that self-defense is OK.
I am fairly sure no one is going hell for that reason, but it might create a scenario where the self-defender also forfeits the greatest of 3 kingdoms of glory. Obviously the telestial standard is to kill whoever you want, and then spend a lot of time in a literal hell to suffer for your own sins. The more killing you do, the closer you get to Stalin and Hitler and other followers of Satan's plan.
I hope I never have to make a decision about whether or not to kill someone, because to me the only allowable reason to kill is if the LORD tells you to do so. Even a direct message from Heaven caused Nephi to hesitate before separating Laban's head from the rest of his body.
I am sure about one true prophet since the days of early Christianity...Joseph Smith. I believe the JST was a mandate from GOD. Our acceptance of this divinely directed manuscript allows us to understand the gospel of JESUS CHRIST more clearly than any other version of the Bible.