Well, a benevolent tyranny is always tempting. Problem is that by being a tyranny you can not prevent it from becoming evil. Human nature pretty much guarantees that what started with good intentions will end up in a way to exploit and subjugate others.

Corruption and greed were already fouling up Yevon's religion, as we saw with Seymour and Kinoc. There wouldn't be anyone to stop it, since the entire population was kept in the dark.