Feedback on "Holy War"

An oxymoron is two words that don’t belong being used together. Why is the phrase “Holy War” an oxymoron? Why is it that so many conflicts in the world today are based upon religious differences yet all major world religions condemn killing?

I think that the phrase “Holy War” is an oxymoron because a war can’t be holy. It’s a brutal thing that takes many lives. It’s the opposite of holy. And the word holy is something that belongs to religion. And many religions say no to wars. But even thought this is the case there are many religious wars going on in the world right now.
It’s hard to say why so many wars are going on because of religion and yet all major world religions say no to war and killing. It could have something to do with many people twist the words, and tell people that it’s ok to kill if it’s for a good cause. I think many people forget about that killing is condemn, and get so absorbed in showing that their religion is better, that they don’t think the whole thing through.