With all the furor going on these days about ISIS, there is a conversation happening about religious extremism. I don't think that religion necessarily makes people more violent: individuals are more or less violent than they are already going to be, and associating that violence with religion does not do service to the good work that religion does in the world.
No, I do not believe religion makes people violent. The four most common religions in the world (Christianity, Islam, Hinduism and Buddhism) all promote peaceful practices. Their religious leaders and icons all lived lives of servitude and encouraged followers to do likewise. Those who practice violence in the name of these major religions cherry pick isolated verses from the religious texts and stretch them in an effort to support the violent actions they were already inclined to commit. People are violent. Religion is simply their excuse.
Religion generally teaches people to love one another and forgive. People who act violently in the name of their religion are twisting things around. They are using only the parts of their religion that they choose to make their point, and try making their violent acts justified. No religion truly preaches violence upon others.
While I realize that many religious issues can make people passionate, passion is not the same as violence. Sure, someone involved in a religious conflict can act violently but I would not place the blame on the religion. If anything, religion in general encourages peaceful and more accepting, empathetic behavior.