A belief system is a way of seeing the world. There are many belief systems, and many ways of seeing the world. The people in each system tend to think their way of seeing the world is the right way for everyone. This is true in both religion and politics.
Most Christians will state their core belief as: "Jesus died to save us from our sins." Yet, there are many followers of Christ who do not believe this. These outliers have been referred to as heretics or as cults. Throughout most of Christian history, heretics were killed, or otherwise silenced. When Constantine sought to solidify his rule of the Roman Empire in 325, he used Christianity as a tool. The Council at Nicea was to create a consistent belief system. Books for the New Testament that aligned with the belief system that Constantine and most bishops wanted were put into the Bible. Those that did not align were destroyed. Fortunately some were hidden. The Christian Bible was created out of a political need to secure power. To be clear, it's not that the Bible was bad, it was limited to those teachings the majority of bishops and politicians wanted people to believe.
There were other ways of following Jesus, but people were not free to practice those. By 380 Christianity was declared the religion of the empire. From that point on heretics could be excommunicated, imprisoned, or killed. The first heretic was executed in 386. The religion whose members had been persecuted then became the persecutor. For the next 1600 years millions were killed in the name of Jesus.
Once the Reformation took place, Protestant authorities followed suit burning and hanging accused witches and conducting pogroms against Jews, who were considered heretics by Marin Luther and others.
Today we see Islamic countries making blasphemy against the law and punishable by death. People who have opposed the prophet Mohammed have been condemned to death or attacked and killed. Example: Salmon Rushdie (condemned) and Charlie Hebdo (Attacked and killed). Fortunately, we seldom see Christians killing others because of opposing beliefs, with the exception of skinheads and the KKK. However, it has only been twenty years since it stopped. (Serbian Christians killed and raped their Muslim neighbors in Kosovo in the 1990's.)
Everyone has the right to believe whatever they want. When your beliefs turn into an attack on others, whether that attack is in words, physical violence, or using the law to exclude people from their rights as citizens, it is still an attack. The Bible, the Koran, and the Torah were not meant to be weapons to destroy non-believers. They were to guide people into a closer relationship with their Higher Power. They are pathways to God. Follow your own path, and let others follow theirs. You have no idea that your path would be better for another person. You certainly may invite them if they are in need.
It's time we moved beyond spiritual and religious arrogance and focused on living as our best selves and challenging ourselves to grow spiritually. We don't need to respect each others' beliefs, but we do need to respect each other. I may think your beliefs are insane, but I can still treat you with great respect. I can choose to see you, and everyone, as created in the image of God. There are no heretics. There are people, and we disagree. As long as disagreement doesn't have you harming others, it's okay.
William Frank Diedrich
Author of Human Adulthood: A Spiritual Romance