Zealots are so fanatically devoted to their political, religious or philisophical beliefs that they fail to acknowledge or respect other points of view. Self-righteous, they see the world in black and white and loathe the concept of compromise.
Zealotry feeds on ignorance and zealots know that large segments of the population are poorly educated, either by choice or due to the failure of society. They thus target their message to this receptive audience, promising personal benefits to the faithful and warning of threats from non-believers and the established government.
Though we often relegate the title to extremists in human society, zealots are readily apparent in the current Republican primary field, as many of the candidates appeal to an undercurrent of racism, evangelism and militarism among their legions. Cooperation and compromise have become anti-American and any hint of thoughtful engagement is dismissed as the tool of liberal intellectuals.