I do not understand what is so irrational about criticizing left-wing sectarianism, of which Nader is but one example. The propensity of the Left for form myriad of sects and cults as a vehicle - or perhaps a donkey cart - to win the US presidency is silly and lamentable - but otherwise, quite innocuous and irrelevant, so it can be safely ignored. It becomes problematic only in a close election, where it may become the proverbial straw that broke the camel's back. In such situation, one would expect otherwise intelligent people to forego their ego trips infantile urges to form mutual admiration societies, and sacrifice their inflated ego and ideological purity for a greater good. It does not seem much to ask.
Left sectarianism already contributed to the rise of Hitler. Now history repeats itself, not quite as farce, with Bush. It does not seem much to expect otherwise intelligent people to learn from history. What is so irrational about criticizing those who can't or won't?
Wojtek