A religion is not necessarily violent. There are realistic religions, belief systems that ignore the “God question” and advise peace through pacifism. That said, by far most religions teach people that believing without evidence is a virtue that will lead you to the absolute truth.
Irrationally constructed realities created by religions are impossible to demolish by rational evidence and someone in power can easily alter anything in that irrational reality without having to prove the amendment.
Needless to say, the vulnerability cause by irrational reality is often misused for political purposes.
If a religion claims to know the unfalsifiable absolute truth then it also suggests that all other religions are absolutely wrong, which creates a convenient environment for politicians to cause divisions in society, create common enemies and make good people do bad things.