My view is that underlying the so-called left-wing is secular humanism, as formulated initially by the ancient Greeks and as recaptured in the modern period.
Humanistic anthropology may not posit that we're created in the image of a perfect deity, but a naturalistic basis of human rights blocks John Gray's pessimism. I'm aware there are skeptics and cynics who say that without God, everything's permissible and that naturalism entails nihilism. But their case isn't so clear.
Also, we mustn't assume the current craziness of American progressivism (cancel culture, etc) represents all the possible alternatives to conservatism (to animality).