I've seen it in the libertarian movement. Some libertarians will denounce an FBI raid and a traffic ticket with equal vehemence. By working themselves into a "more libertarian than thou" fervor, they feel self-righteous, even holy.
For such people, politics is their religion. They derive their sense of self-worth from the purity and fervor of their activism (even if that activism is limited to posting on message boards). It's especially true of Leftists, but also true of many libertarians, and even some conservatives.
Some of us believe what we see/hear and are speaking to that truth. Stop trying to shut up those who disagree with you.