Most of the real world's Empires of the past brought about real and positive changes in knowledge, technology, and commerce. Were they all "evil?"
Whether the good the empire brought outweighs the things it did to become and stay an empire is a difficult question. If any outsiders or citizens got in the way they certainly did "evil" to them.
Some more evil than others, ofc. The Persians would let conquered peoples keep local customs as long as they dealt honestly with them - the punishment for dishonesty doesn't bear thinking about. The mongols would give you a chance to surrender but it was often almost as bad for you as resisting. Pax Romana... aye, it's peaceful when the belligerent city has been leveled to the ground and all survivors taken away as slaves. Alexander's empire might have spread the most "good" from our POV, what with exporting hellenistic culture so far away.