Erich Fromm is one my favourite philosophers of the 20th century:
“Optimism is an alienated form of faith, pessimism and alienated form of despair.”
Erich Fromm
I also like Fromm, he held some strong Marxian positions the following from Marx's Concept of Man by Fromm:
"For Marx, as for Hegel, the concept of alienation is based on the distinction between existence and essence, on the fact that man's existence is alienated from his essence, that in reality he is not what he potentially is, or, to put it differently, that he is not what he ought to be, and that he ought to be that which he could be."