On the surface, liberals appear to be neurotic, guilt-driven people prone to auto-flagellation. This guilt drives them to think they're a plague on the planet, and that everything they do is bad. So they subjugate humans to animals, restrict any form of human activity that might affect the environment, advocate population control, castigate the rich and successful, apologize to other countries for everything, etc. Self-loathing is like a religion to them.
But when you dig deeper you generally find that in actuality they don't think badly of themselves...they're actually very self-centered people who think badly of you. Population growth has decreased elbow room between people, and they're asserting themselves by seeking to control those around them. This is why most activist liberals originate in urban areas. Guilt is just the primary tool they use to convince people to back down and succumb to their will. Guilt is a negative motivator that masquerades as something positive. It's not about animals or the environment, because these people rarely interact with the outdoors. It's about power and control...the desire to dominate other people.