Whatever society you live in, that biases your view of religion. You view the dominant religion as harmless, and people who believe in it as normal people. You view other religions as suspicious and people who believe in them as abnormal. In a Christian majority country, people see Christianity as normal and Islam as a threat. In a Muslim majority country, people see Islam as normal and Christianity as a threat.
Example: if a billion believers tell you, "This is a religion of peace and we reject violence," but you find a passage in their holy book endorsing violence, what do you conclude? Is it a religion of peace or of violence? Also assume their fellow believers have fought countless wars over the years, but most members of the religion just want to live their lives in peace.
In this case, most people apply completely different standards depending on the religion. In a Christian majority country, people will tend to say that Christianity is a religion of peace. They justify it by talking about all the great things Christians done, and how most of them are peaceful people, and quoting Bible passages that endorse peace. But they say Islam is a religion of violence, citing terrible crimes committed by Muslims and quoting passages from the Koran that endorse violence.
But you can just as easily reverse those. Countless terrible acts of violence have been committed by Christians. The Bible has lots of passages endorsing violence. Most Muslims are peaceful people, and describe their religion as one of peace. And in Muslim majority countries, people see the two religions in the exactly reversed roles, based on exactly the same evidence, justifying their conclusions with exactly the same logic.