Despite being a terribly uncommon situation, my biggest fear is one of those middle of the night, oops we have the wrong house, no-knock warrants. If a bunch of people break down the door yelling and screaming in the middle of the night, there's no time to sit around and try and figure out if they're friend or foe. You're going to assume, by virtue of the fact that they just invaded your house and are coming at you aggressively, that they mean to do you bodily harm, causing you to fear for your life, and you therefore open fire. Hopefully they really aren't just confused Police serving a no-knock on the wrong house...