Actually that's one of the 10 Commandments, and it says "Thou shalt not murder."
Killing is something practiced and condoned and advocated in the Bible, it's just 'unjustifiable' (as in cold blooded) murder that is wrong. What's the Bible about? It's not exactly celebrating fellas who made really good soup and knitted some fine cloth. It's mostly about heroes who slay (mainly) the enemy and a bunch of other heinous crap. Lot is a favorite. Given what he did ("Here, rape my teen daughters, they're virgins!" Later, "Hey, sis, let's get daddy drunk and take turns raping him so we can get pregnant because there are no more guys around!") I hate to imagine how bad Sodom & Gommorah were, because, yeouch.