If they weren't mentally ill, they wouldn't be "liberals."
Anyone as angry and filled with hatred as these people is OBVIOUSLY depressed.
It's hard to say whether the chicken or the egg came first, but their sick world-view could only produce depression, anger, and hatred, and it could only be accepted by the mentally ill.
I agree - there's lots of area here to wade through in determining correlation and/or causation. That said, IMHO, one can not embrace liberal ideology without denying facts and cold hard reality.
At its core, liberalism believes that imperfect humans in imperfect societies can be herded, coerced and moulded into a utopian state. That this has not yet been achieved is a continual cause of perpetual disappointment and an ever growing resentment and rage for those who (in their mind) stand in the way.