I don't think it makes sense to trace a single psychological/character/personality trait as the cause of political beliefs. How do you like it when they do that to us?
Progressives have a lot of notions in common, but they can arrive at them for various personal and environmental reasons, including that that's what the people around them and raising them believed. The most common thread seems to be a belief that sublime, transcendent abstract entities like "society" or "the international community" are not merely metaphoric tools for describing people's interactions, but are actually more real and more important than real live individuals; that these abstractions have more agency and authority than all individuals put together.
This is supported by the common sayings, valid in some ways and dangerously wrong in others, that things are "greater than the sum of their parts," and that people should live for "something larger than themselves."
A contempt for individuality, for individual rights and responsibilities, is more a result of this than a cause, and for some liberals it presents an irrepressible conflict with other truly liberal beliefs that they have drawn from their patriotism, religion, or just from being thinking and humane people. That's the stage I was at for a while, when I didn't know anything about economics, but I could tell that the government wielding economic power over people would constrain their political freedom.
-- John Crouch, responding to the great Robert Bidinotto, who wrote:
UNDERSTANDING THE LEFT. After nearly six decades of direct experience, observation, and study, I have come to some firm conclusions about the ideological left (as opposed to those "liberals" who are simply compassionate toward others). I think it all revolves around the left's war on self-responsibility. They HATE that concept. In their worldview, if you create something good in the world, "You didn't build that"; but if you do something bad, "You couldn't help it." Either way, they HATE the notion that anyone (meaning: themselves) should be held accountable for their status in life. ... Ideological leftism is all, only, and *always* about advancing the Narrative of Personal Irresponsibility. It is the morality play that holds individuals responsible for every other man, woman, child, tree, plant, animal, or degree of temperature on the planet...but not for *themselves* as individuals.