Peter Kropotkin was surely on the left. He was one of the founders of what is now called 'sociobiology' or 'evolutionary psychology' with his book Mutual Aid, arguing that human nature had evolved in ways conducive to the communitarian anarchism that he espoused.
Noam ChomskyPeople don't talk to each other. You're alone with your television set or internet. But you can't have a functioning democracy without what sociologists call "secondary organizations," places where people can get together, plan, talk and develop ideas. You don't do it alone.
Noam ChomskyAny little issue - Miss Universe, or whatever it may be - [Donald Trump] is completely unpredictable, he'll go off into outer space.
Noam ChomskyIf scientists and scholars were to become "collectively self-organised and consciously activist" today, they would probably devote themselves to service to state and private power. Those who have different goals should (and do) become organized and activist.
Noam Chomsky