Christians: Why is it so hard for us to accomplish unity?

Most Christians don't practice what they preach. They believe in unity and peace yet force their beliefs on others who don't want to share in those beliefs, creating disruption. I think we could come closer to unity if we would just accept and allow others to believe in whatever they choose without telling them that they are wrong and need to change. Just because something is against your beliefs does not mean that is against someone else's beliefs.