The question seems important, since where liberalism comes from affects how we should deal with it and where it is likely to go. Many right-wingers, for example, think of it as psychological or instrumental: people are liberals because they feel this way or that, or because they want to get money, power, status, or whatever. Such views suggest that liberalism need not be taken seriously on its own terms, and will disappear when events shift the balance of advantages or put people in a different mood.
My view is different. I see liberalism as conceptual, as a manifestation of a peculiarly modern (post-scientific revolution) way of making sense of reality. It’s the logical outcome of fundamental modern concepts, and will last and keep on developing on its own lines as long as modernity lasts. That’s why liberals not only believe that they are right, but that people who disagree with them are irrational, demonic, mentally ill, or whatever. That means liberalism is very durable, and we had better be prepared for a long battle fought at a very basic level.
The claim liberalism is basically conceptual is not the claim that “ideas run the world” in any very immediate sense. It’s concepts that matter, not ideas. Concepts are habitual ways of sorting things out, ideas are descriptions or proposals regarding how to do so. The difference is the same as the difference between grammar in use and descriptive or prescriptive grammar.
Metaphysics and epistemology in use, like language and grammar in use, are basic social institutions that are absolutely fundamental to how people cooperate. For example, they make it possible for people to talk to each other about complex matters. As basic institutions, fundamental concepts become authoritative the same way other basic institutions become authoritative. The process has more to do with how society functions and how people deal with life in general than particular feelings and interests.
At most times people just take basic concepts for granted, but there are usually degrees of adherence. There are insiders who harbor secret doubts and outsiders who grumble. Also, psychology, material advantage, general frustration, or whatever can cause people to emphasize or downplay this aspect or that of their society’s basic outlook, or decide that some modification or change would improve things.
So long as the system remains functional none of that makes much difference. Sometimes though there are problems with existing concepts. They don’t seem to work as well as some alternative, or influential people may find they like new ones and adopt them for whatever reason. The effect may be development of a subculture or sharpening of existing subcultural differences. Over time the result may be to revolutionize the whole system.
The most recent revolution was the modern one, which involved, at the most fundamental conceptual level, the attempted rejection of formal and final cause in favor of exclusive reliance on material and efficient cause. That revolution was closely related to the rise of modern natural science, modern capitalism, and the modern state, and involved a great increase in the social emphasis on control. (How such things come about is a complicated story that can be told various ways. Etiologies have their own etiologies.)
So liberalism isn’t caused by the psychology or particular interests of particular people, any more than the patria potestas or divine right of kings were caused by the psychology or particular interests of particular people. What people find authoritative expresses their whole way and view of life, which is normally rather stable and impersonal and goes very deep.
That view of the matter directs attention to the effect of liberalism on character more than the reverse. Liberalism starts with a technological understanding of reason that makes rational conduct a matter of getting what you want. That understanding tends to make people manipulative, self-centered, dishonest, etc. The technological understanding of reason also includes formal rationality, which leads to the reflection that if desire is the standard of the good then all desires of all agents are equally desires and equally deserve satisfaction. That reflection leads to altruism. Hence a characteristic psychological type, the altruistic sociopath. Examples would include Shelley, Rousseau, and various left-wing social reformers. That psychological type corresponds to a social ideal of maximum equal preference satisfaction technologically achieved, but it is much more the result than cause of that ideal.