The truth be told, I don't really believe that.
Now, I do believe that many conservatives get their basic facts wrong, misread history and maintain a worldview that's out of touch with reality. But are they "sick" people in a general sense? No.
That being said, the recent conservative meme "Liberalism is a mental disorder," which I've heard many times, most recently last week from two conservatives I know, is becoming tiresome. It's very hard for me to take seriously a mentality that refuses to engage folks that don't agree with them.
The clause is what's known in psychology as a "thought-stopper," meant to end conversation. "We know what we know what we know ... " without bothering to consider alternative views or explanations.
Do liberals criticize conservatives? Sure they do but based on how conservatives behave, not on what they believe. In fact, it could be said that how you behave is a reflection of what you believe. (Which is why more and more "liberals" are disdaining conservatism.)
Recent complaints about President Obama -- that he's "weak" and/or a "tyrant" -- only inflame, never inform. Worse, they're never specific as to what he does except for the Affordable Care Act (which is law, by the way), his use of executive orders and his lack of what they see as a credible response to the situation in Ukraine. What would you do? they should be asking themselves. But that's beside the point.
Really, those who subscribe to that view ought to think -- think -- about what they believe and not assume that they alone know the right answers. Such arrogance buttressed by fear is what's causing the dysfunction in American political discourse.
"But we need to combat Marxist/communists/socialists ... " No, you don't, because if you knew what they really believed you might realize that they could be right. So stop slinging mud and start talking to people who don't support your ideology; you might learn something.