I ain't a Bible scholar but I seem to recall that those Old Testament Israelites rubbed out a bunch of peoples just because they were there and God commanded them to be rubbed out. Presumably they were slaughtered for their own good and the greater glory of God.
I once knew a man from Guatemala and when he spoke of the atrocities committed by the Spaniard conquistadors he felt that it was worthwhile in the end because along with murder, corruption and disease the Spanish missionaries brought the "One True Faith". Likewise, religion was one of the justifications for genocide against the North American Indians.
Some people say that it's religous intolerance that results in the atrocities. But Christians are commanded to be intolerant. Their "Great Commission" is to evangelise the world with their religion, not to tolerate others. And there is precious little tolerance in Islam regardless of the propaganda we read in the newspapers.
If you made a list of the things that have resulted in human mysery religion would make the top ten easily, maybe the top five right up there with disease. Read up on the Crusades sometime--makes modern warfare look like a tea party.