Most liberal puppets do suffer from a certain form of delusion, to be sure; saying "liberalism" is a mental disorder is a little too broad, though, since the liberal leaders are not delusional--they know exactly what they're doing.
I used to consider these people as merely the "loyal opposition"; today I see them as the enemies of freedom. We are engaged in Civl War II in this nation. Some call it a culture war. So far it is a war of words. It has not become a hot war - yet. Massive civil unrest can still be avoided; but time is running out. The economic reality of trying to sustain an unsustainable welfare state on the backs of the working American is going to become apparent soon. When that happens all bets are off.
I would suggest that although converting liberals will be difficult, recognizing the nature of the disorder and undermining its roots can pay massive dividends. If just a few liberals here and there convert, then those that remain can view them as 'sell-outs'. If, however, more start converting and seem to become happier and more successful as a result, more and more liberals are going to start wondering whether maybe they too shouldn't see what it is these other people are 'getting'. I don't know for sure whether critical mass is achievable, but if it is I would suspect the counry could shift from being nearly 50-50 to being 80-20 in a pretty short time.
In my experience, the makeup of many liberals consists of altruistic motivation combined with fear of abandonment. They generally have a passion for making the world a better place, which I admire. But, such a person seems pathologically incapable of understanding that in order to achieve the best possible world, people need to be left free to make their own choices. Perhaps the source of the pathology is a parent who chose to leave them, either physically or psychologically. Maybe it was their own decision to separate from their parents, and their unrealized regret unwittingly actuates their behavior. Perhaps it was abuse of some sort. The psycholgical trauma seems to always involve rejection by a parent, usually a father.
The common thread for this type of liberal seems to be that the fear of being abandoned is transferred to governmental policy preferences which promote social welfare. The government becomes the all caring parent that will never leave and will behave serviently to satisfy the needs of everyone. It is almost impossible to reason with this type of unrealized fear.