To me, the best part about Fallout is if theres somebody you hate, you can kill them. Way different and more fun than those games where your weapon just passes through them.
Yeah you can kill NPCs if you want but you have to deal with the slow crawl of the angered towns people depending on the situation. That's all the deterrent I needed. Watching a bunch of zombie looking NPCs slowing shambling to my position was agonizing. It's better to save the killing of the innocents for towns with no law or in areas where no one will notice.