The extreme left is just as crazy as the extreme right, except that there's like 100x more people in the extreme right and they're taken much more credibly as a voting bloc. Are there any 9/11 conspiracy theorists who actually hold office? Tea-baggers are winning actual elections. They may be primary victories, and will prob lead to delicious defeat in November, but the left has not been nearly as successful nominating brain-dead delusional candidates or motivating en masse to defeat moderates.
And to you who would respond "[cough] Alvin Greene [/cough]" I say, good point, great job!