Prefect

Think of it as... Imagine you're in a shopping center, and there's something really, really bad outside, and you don't want your children getting hurt by it. So you lock the door and distract your children with the things in the shop, but if they try to leave? Or if they try to convince the others they need to leave? You have to stop them. Because if those door opens and what's outside gets in-- then the bad thing is everywhere.

So you protect them, and they kill you for it.