The Empire has many external and internal problems. The Emperor is infallible and always right. But there is a force above him that can make him act within strict limits. And those limits prevent the Empire from contacting underdeveloped civilizations until they reach a certain level.
But what should be done if eight billion people on a border planet, only just beginning to explore space, are threatened by rapid and guaranteed destruction? You could simply sacrifice them and forget—after all, a law is a law. But if you really want, you can find in any law at least a narrow loophole where a couple or three hundred warships can squeeze through.