I fear it's because religion is man's attempt to reach God, and when he feels he has succeeded, he cannot abide anyone else's claim to have done the same.
“All along we find that social life - religion, politics, art - reflects the stages reached in the development of the knowledge of self; it shows the social uses made of this knowledge.”
“Science without respect for human life is degrading to us all and reflects a hollow and deceptive philosophy, a philosophy that we as a people should never condone.”