Human nature is a mixed bag so this isn't unreasonable. But it's amazing how they've managed to establish an image of optimism, especially given what liberty-hating shrill moral scolds they are. Liberals are optimistic about the possibility of humanity's redemption, but only through a benevolent tyranny of liberals. In other words humanity can be trained if it will submit to the leash.
I think that this is one area that AG missed. The left does have a pessimistic vision of humanity. However, they also seem to think that with enough of the “whip,” via government control, that humanity is somehow perfectible.