We might identify a class of violence we call ideological violence. We can start be identifying overall worldviews. These might be religious, in the case of Judaism, Christianity, and Islam, or Hinduism, etc. or these might be materialist, or what have you. Then we might ask how much we care whether other people believe what we do. As humans we like to see people believe what we believe. And here there is a huge amount of variation in how much we would like to see others agree with us. Some Christians are really motivated to see everyone else become a Christian, others care a whole lot less. Some Christians think salvation is at stake, since the only way to be saved is to believe as they do. Others think God's grace can save nonbelievers (see the documents of Vatican II as an example). Atheists are the same way. Some atheists think belief in God is a "mind virus" we've got to cure for the sake of civilization, others have no interest in whether others believe as we do. Usually theism or atheism isn't the whole of what we would like people to believe. I don't know of any believer in God who thinks belief that God exists is necessary and sufficient for salvation. Now, caring a lot over whether other people believe as we do doesn't necessarily mean we will use force to make sure they do. we might decide that it will do more harm than good for our cause. To use violence, we have to think it will work, and that it's appropriate. Theism and atheism are not answers to the question of the meaning of life, but they are necessary conditions for ideologies that some people think are the answer. Communists for example, thought that religion had to be destroyed so that we could achieve the classless and stateless society.
There is a road to ideological violence whether or not you believe in a god or not.