There have been false doctrine and false teachers since the church started. The same heresies exist today. There were false teachers that followed the Apostle Paul around and when he would leave town they would go in and say the Apostle Paul was a false teacher and work to convert them to their doctrines. This is why the books of Galatians & I Corinthians were written, John in his small books talked about false teachers, Jude is written about the damnation of heretics and fallen angels, etc. etc.
The Apostle Paul stated in Galatians that even if an angel come and teach any gospel other than what they had received from him, let him be accursed (anathema, eternally damned) and for emphasis he repeated it. Jesus railed on the religious leaders and told them they would receive the greatest damnation. This mamby pamby Sunday School view of Jesus walking around carrying a sheep under one arm and patting the little children on the head is not a scriptural. We are called to defend the faith, there is only one way to heaven and the eternal future souls lie in the balance. There's a heaven to gain and a hell to be shunned. False religion is Satan's greatest tool because man has an innate need to worship something, and if you don't stand for something, you'll fall for anything. I am always amazed that when people reject the truth, there is no limit to what they will believe.