If it wasn't for people believing the fantastical worlds that were supposedly coming their way, as well as the witches and goblins that were supposedly threatening them if they strayed, there wouldn't have been the Crusades - they killed a few people, or the Inquisition - that knocked a few off as well......
I disagree entirely. People always find ways of creating in groups vs. out-groups. If you asked any Muslim during the Crusades what it was about, they would reply it was about the Franks trying to reconquer lands that the Arabs had won. They wouldn't say it was Islam vs. Christianity. The Frankish soldiers may say that, but that's because of propaganda efforts by the Pope. And chances are the soldiers were not so pious anyway. They'd probably say they were fighting to win glory and bring back gold. The real reason for the crusades was so Europeans would stop killing other Europeans. The Pope used religion as a uniting tool and picked an enemy that was threatening and lived far away.
As for the Spanish Inquisition, that was more about uniting Spain. Remember, it started immediately after the marriage of Ferdinand and Isabella. Some of it had to do with the Moors, but they were the "other" to help create a Spanish identity.
In order to have an "us," you must create an "other." It's basic human nature. Religion is just the tool used to act it out. If it wasn't for religion, it would be something else.