Leftism vs. Insanity

It's both.

Leftists lie all the time, which drives them crazy.

Leftists are enablers. If you are crazy, you're attracted to leftists because of the gimmedats and because they'll flatter your paranoid delusions. "Fornication isn't bad for you! It's those mean nasty preachers who are making you feel bad!" "Don't worry, there's nothing wrong with being a cripple mutant." Those with brain problems are typically even less robust than average and thus even less able to handle the truth.

Flattering the delusions aggravates the underlying condition, which makes the madman more loyal. There's obviously no place for them on the other side of the aisle (blues are gay so reds have to be ultra stoic and never show any feeling except outrage). Even should reds get over themselves and address the problem, the crazies will suffer from paranoia and see a trap. The leftists will flatter this delusion as hard as they possibly can. 

In the unlikely event that someone who basically not a mutant should adopt leftism, the lies will increase their internal stresses and reduce their ability to deal with stress, until something breaks. Turns out pretending not to have that need is not a viable strategy.