Christianity's a big one.
I don't know... ohh wait... nevermind I am thinking of another religion.
Anyhow one of the ways of looking at it is that any religion is ultimately an institution with people.
Why would two buisnesses fight eachother even if both of them boast great ethics? Why would two nations fight eachother when they both boast peacefulness?
Oddly enough a lot of the time the reason for "religious" wars couldn't be further from religion and are often for geopolitical gain (Heck the Crusades is often considered the largest most deadly religious war in history and yet the practices including razes and convert or die were adopted for use in the crusades but were otherwise common practices). It is why I often consider any statement of "Religion causes wars" to be silly.
So what specific "High-moral" religion fight are you refering to anyhow? and by High-moral I assume you mean a religion with an actual moral docterine your expected to adhere by.
Why does power corrupt?
Often it doesn't. However we can equate a person to a dam. When there is no water a dam stands as if it is strong. When there is water the cracks and holes become all the more obvious.
Power makes all the faults in society and people all the more noticable. As well for the most part corrupt people are the ones who know how to get the power while humble saintly people tend to barred from such.