Historically speaking, the effect of every religion on human society, when it comes to considering the effect of the teachings of the Sources of every religion, has been a positive one and cause of tremendous growth in society in every instance.
In time we, humanity, however tend to distort religions and sway them to our own causes.
What I am trying to say is that if the Founders of the world's greatest religions were to exist with one another today, their teachings would be in agreement with one another and they would still preach the same "love thy neighbor" and "speak the truth" that they always have. They wouldn't be at conflict with one another, because the foundation of every religion is one when it comes to the basic teachings and principles... which religion is out there that says we should not be truthful? or that we shouldn't love one another?
The unpleasant parts of religion we might witness today (fanaticism, teachings to cause division among people, etc.) is a result of the distortion of the original teachings in time and through us.