Jesus was consistently cheerful, notwithstanding he sometimes drank deeply of the cup of human sorrow. He fearlessly faced the realities of existence, yet was he filled with enthusiasm for the gospel of the kingdom.  Jesus pointed out that overmuch sympathy and pity may degenerate into serious emotional instability; that enthusiasm may drive on into fanaticism. 
And in welcoming Simon as his second apostle, Jesus said: “Simon, your enthusiasm is commendable, but it is dangerous to the work of the kingdom. I admonish you to become more thoughtful in your speech. I would change your name to Peter”.  Apostles must be possessed with zeal and intelligent enthusiasm. 
The religious enthusiasm with which social reforms are sometimes propagated has the great weakness that it is unable to profit from open religious criticism and thereby attain to profitable levels of self-correction.