What a thread...
To be honest, there are mainly two kinds of psychology, which both divide to several branches (search wikipedia if you want to know more).
First, there is the "traditional" psychology that tries to understand and define in abstract terms the inner workings of human mind on both conscious and subconscious levels. There are many approaches on this kind of psychology.
Then there is neuropsychology, which aims to understand how the structure and function of the brain relate to specific psychological processes that are defined by traditional psychology. It is closely related to neurological research, which is undisputedly scientific, and whatever one may think of traditional psychology and its scientific integrity or lack thereof, one should recognize the solid scientific basis of neuropsychology.
Neuropsychology works as an important link between psychology and psychiatry. Psychology in general is science of mind, while psychiatry is the practical medical science that aims to help people with mental problems.
Obviously, there are several approaches to that goal too. One of them is "chemical approach", which is most closely linked to neuropsychology and neurology. Many psychiatric conditions are a direct or secondary results of brain malfunction, like for example clinical depression which is characterized by lack of serotonine. Other approaches include psychotherapy and other more traditional treatments, which can be equally efficient as chemical approach, and in many cases even better. Regardless of how different psychiatric conditions are treated, lack of will power is more of a symptom than cause of disease in 99.9% of cases. The rest is statistical noise.
Okay, thats my part of trying to extinguish the flames on this thread about psychology. Back to actual topic.
So, levels of moral reasoning.
I postulate that most social conservatives are mired in Level 2 thinking, while most social liberals have attained level 3 reasoning.
I'm not sure of that kind of generalization. As you menton yourself, many people never reach the third level of Kohlberg's scale of moral reasoning.
I don't doubt there are many social liberals that have their values just as locked as conservatives, but just in different direction. In cases of people who don't go beyond conventional morals, the moral structure of their mindset depends more of environmental factors: home, friends, so forth. So, those people who don't go beyond level two and have conservative background end up having conservative morals (no surprize there), but also liberals' kids who don't go beyond level two end up having liberal set of moral beliefs.
After all there are bound to be just as fundamental liberals as there are fundamental conservatives. By fundamental liberal I mean people who have liberal values for the sake of them being liberal values and not because they've thought through matters and built their moral structure by themselves. So I don't think it's valid to say that "people who get into 3rd level end up being liberal and those stuck on 2nd level end up as conservatives". However, it might be useful to research how backgrounds affect on development of moral reasoning - whether the background and environment encourage or discourage it.
It's entirely possible and plausible to speculate that conservative environment doesn't really encourage people to develop their own moral structure, as there already is one set of moral beliefs that most people around (at least seem to) follow. However, liberal environment can do this to a kid also. I actually think that growing up in a diverse environment that has different sets of moral beliefs around will most likely lead to a person developing his or her own set of beliefs more often than growing up in an environment where everyone have same opinions about something. Controversies may help one to understand that there might not be one and only hole sacred opinion of God to follow, or alternatively that the most liberal option is not necessarily the best one in all cases, which would eventually lead to level three moral reasoning, when person forms his or her own opinions about things and acts accordingly.
So, I'd say that the percentage of people on levels 2 and 3 amongst liberals and conservatives is probably not that different. There might be slightly more people on level three amongst liberals, but there sure are "locked-minded" fundies on both groups, people who have conventional morality adjusted and fastened to the dominant morality set around them.
So, in short.
Level of moral reasoning doesn't make one something, and being something probably is not a good indication to defining one's level of moral reasoning either.
However, unilateral exposure to a certain moral structure - be it conservative or liberal - is likely to lead to adoption of that particular moral mindset, while being exposed to many points of view and multiple sets of morality, ie. learning to know different kinds of people, is more likely to lead to realization that one set of moral beliefs is not necessarily better than another, which would likely lead to post-conventional moral reasoning.
That's my view on this subject.
Then there is the question of whether or not postventional morality is "better" than conventional morality, or whether or not they contribute to worth of a human. I'd say the level of moral reasoning doesn't effect human worth, but it can affect the integrity of person's argumentation. Conventional morale easily falls into the same pit that those proverbial "ten billion flies that can't be wrong" came from. Arguments based on post-conventional morale do not face this problem - their worth is directly proportionaly to the aptness of the argumentee.
