I like reading through the more esoteric branches of religion as they typically eschew the large centralized structures and strict social controls seen in larger religions. The ideas presented in things like Sufism, Kabbalah, or Gnosticism are usually focused around rejecting material consumption and can often align pretty well with leftist values. You could even look into Mazdakism, which was a branch of Zoroastrianism that focused on radical social change and equality that some people have likened to a primitive form of communism.

If you're into deism and animal liberation a great poet is al-Maʿarrī, whose actually been featured in one of the megathreads.