If religion did not exist, people would use other excuses to try and justify their hate and violence so people will follow them, its as simple as that. However, many people don't consider it as such unfortunately because they either are quite narrow minded on many topics or they've had first-hand bad experience with people who say they do something because of religion. It is a difficult to task to change the views of many people but the more open-minded people remain, the further we will go away not only from the misconceptions about religion but fanaticism for those who still choose to follow it.
Most all religions have some peaceful roots both in their origins and core beliefs. They did not originate randomly when someone dreamed of world domination through the generations. It is when the religion has become so ingrained in the people of society that negative forces see fit to use that strong passionate belief to give them control. Overtime that merges with the beliefs and practices and it seems as if the religion is the dominating force creating all the trouble when in fact, even if it has become so, it was not always like that and it was made that way by outside forces of corruption. Its just put up as a face for the most part and the other part involves things being put in to the religion or created.
If religion did not exist, there would still be some strong motivating beliefs and ideas out there to manipulate by corrupt people. Those ideas, very basic ideas like love or compassion could even be twisted into being evil and wrong when it is only bad people creating that corruption. So it is quite flimsy to suggest religion is the
cause of all problems in the world, the root of all hatred, or the reason for histories wars. History is filled with examples where something else started something and then the religion was used to rile it up further because the main reason was too complacent to act on.
Another way to look at it is to look at other reasons wars were initiated in our world. European and American powers fought Native Americans for many years, breaking treaties, taking land, forcing them to migrate further and further west, etc. That wasn't simply motivated because they didn't believe the same as they did, they also had a different skin complexion. The colonization of Africa by European powers and the breakdown of China and its kingdom through spheres of influences and drugs was followed by a wave of religious zeal but the oppression was started by it. Knowing all this, you wouldn't say that we should abolish all cultures or make people breed so much that races don't exist. One, that's genocidal and two, it destroys an important aspect of humanity, that is it's diversity. Same way, religions all hold different views and ideas of the world but only those that choose to use it and corrupt it without remorse for their purposes will sacrifice it in the peoples minds. Blaming it and calling for its abolishment would serve no purpose.
As I said, history is filled with these examples. The most basic way to look at it but also the most time consuming would be to look at every war and its causes and the reason for each side fighting. I have looked at many wars including so called religious wars and could not truly find religion ever being a cause of any fight. Even the Crusades can be seen as the Papacy trying to increase prestige, land, and influence by starting a full scale war against the biggest threat to Europe at the time; its like Hollywood making movies capitalizing on the tension of the Cold War by making movies about Soviets being evil monster bad guys against the US. No one would say that Hollywood was being very patriotic by making these movies, they just wanted a good villain for movies to make a lot of money.
To talk about more current events and central examples of the fallacy that religion causes all problems, people in Muslim countries didn't like their corrupt politicians and governments, their lack of resources, the debts they had gained from western powers, the long gone days of glory the Muslims had, etc., not that the West was Christian or Jewish. That was made to exacerbate the hatred but it certainly didn't start it. Any fighting that has happened between the Muslim countries themselves has occurred through Western Power meddling from the end of the Cold War.
They upset governments and peoples there for many decades to counteract the influence of the Soviet Union. With the fall of the Ottoman Empire, they also divided up the region into their own countries with their own royal families and petty disputes so that there would be little hope of reconciliation and reemergence of a strong Eastern Power such as the Ottomans and others who had been a pain for the Europeans for many centuries. Once they started overcoming that and other problems started emerging from continuous outside influence in other forms, they just went over the edge.
To gain some unifying force for violence and retaliation, those who chose to terrorize used the common religion of the people because it was a strong ideology that had not faded so much as it had in the West. Corrupt governments certainly didn't care as long as their rule was kept intact and whatever deals they had with strong foreign powers was kept. Current events show however that the people are now getting fed up of even that. Governments fighting amongst each other too use it. Both sides in the Iran-Iraq war said their people would go to heaven for killing the other and they would go to hell even though both were Muslim and both had a considerable population of either denomination who fought, Iraq does anyways.
I hope that clears it up some for many people, I spit it out as I see it and as it comes to mind so its not always organized or even very considerate sometimes so I'm sorry if anything offends anyone.