I would say you're half right. The problem isn't that leftists are lunatics or irrational. The problem is that they place too much an emphasis on authority and not on the facts themselves.

Authorities (the media, politicians, certain doctors, organizations) tell them which facts are true, so they have a knee-jerk reaction to anything that disagrees with their "true" facts.

The key is to pit the organizations against each other and then they'll be forced to look at the facts themselves.