It can definitely be ethical in situations where the general public aren't intelligent enough to correctly interpret the actual information.

If you give them the truth they will act in ways which are detrimental to themselves, so false information can be better.

Thats all Machiaveli really said, he got a bad reputation from misunderstanding of the idea.

A good example is telling communities that a God exists, in order to encourage them to follow the law, put full effort in to battles, avoid food poisoning, etc. This seems to be pretty much why Constantine encouraged the cult of Christianity into a main-stream religion.