"And the point the writer is making, surely, is that domestic opponents of Bush need to recognise the truth of that. If you want to destroy the corruption of what America could be which is represented by Bush and Co, you have to do it in an American way."

On the contrary, I see the author showing that this portion of the left is blind to it's own corruption (each side carries the seeds of different evils of extreme). They also see the right as a caricature that is, ironically, not that different in style from the caricature the author paints of them.