The rapture will occur to get us out of here before it gets that bad. No it won't. That will happen at the end of the tribulation period, at the same time as the resurrection of the dead in Christ. The man of perdition will have already been revealed and the mass executions, by beheading, of the saints who refuse to take his mark will have already occurred. It is wrong to kill the enemy, and if these are the times of the approaching Apocalypse, then it is wrong to resist the evil the Bible says will reign for a time anyway.
Murder is wrong.
Self defense is not. Nor is defense of one's family, friends, property, town, city, state or nation. If such defense requires aggressive action against an approaching foe, it is still defense. You don't wait until the snake bites you before you shoot it, you don't let a scorpion sting you before you squish it. You are within your legal rights to shoot a knife-wielding attacker when he is yet twenty feet from you because it is recognized that he presents a lethal danger to your person.