Intolerance is the result of self-indulgence, and when religions turn their hack on their founding ideals.
A standard thesaurus list of the syn onyms for "intolerance" would in clude words such as "bigotry", "prejudice", "partiality", "fanaticism", "dogmatism", "racism", "jingoism", "sexism", "bias", "injustice", "umbrage", "discrimination", "high-handedness", "narrow-mindedness", "nepotism", and so on. Each of these terms denotes base characteristics that are antitheses to the development of a just and democratic society.
The history of human civilisation has been a continuous struggle to combat various forms of intolerance in individuals, rulers, groups and nations. The more autocratic a ruler, the less tolerant will the establishment be towards the common people. In reverse, citizens are more tolerant towards each other when their society is democratic. Intolerance is at its height in regimes which cannot stand criticism.
We find that many of the eternal stories of the world, the myths, are based on this residuum of reality. Take Greek mythology, for example. Zeus is portrayed as the supreme deity, the symbol of Power, Rule and Law. He is furious at Prometheus for stealing fire from the gods and giving it to man, and for teaching him many useful arts and sciences. For this rebellious act of imparting knowledge to a lesser being, Prometheus is chained to a mountain and vultures let loose to tear his body into pieces.