Evocative of the lunatic fringe, the phrase began existence as a disparaging slur against the "Far Left;" however, due increasing polarization within United States, and an ever-shifting culture war, the term has come to denote virtually anyone with a "liberal agenda," or an aversion to McCarthyism. It is also used within a condescending framework in reference to young, perhaps inexperienced, political dissenters.
While no doubt extremists do exist, the casual disregard for alternative viewpoints, and the implied disdain for Constitutional dissent which simmers beneath its surface, is far more disturbing to the average political theorist than any Leftist dogma, extremist or otherwise, yet to surface.
"Don't call him a 'Commie pinko,' Dad--call him a 'moonbat.' Awww...look--he's cryin'! Maybe he'll go hug a tree."
Though originally a term denoting an internet spoof-religion, akin to Recreational Christianity, it has, through common usage, evolved into more of a disparaging slur against jubilant fundamentalist Christians in general, and Charismatic Christians in particular. It is aimed at those whose over-simplification of Christian dogma appear to, in all actuality, complicate it. It is a way of saying "You're world-view is so far removed from conventional reality, that you are not even worth debating." Synonymn: clicker.
"I hate to condescend like this, but with your obviously Dake-Bonoist views, I may as well be discussing politics with Jimmy Swaggart."