Psychology is slow to catch up with modern philosophy, which started with Descartes in the seventeenth century with his cogito ergo sum, or “I think therefore I am.” Freud modeled his theories on ancient philosophy and drama, mostly Plato and Sophocles, and the psychological tradition followed his lead. Psychology is just now beginning to admit the contributions of more recent philosophy such as existentialism. Sartre was essentially a Cartesian in the way he started from the point of view of subjectivity, of individual consciousness. The ramifications of his thinking were the condition of freedom for all individual human beings. He denied the determinism of nature in the case of humanity: humankind was an end in itself, determining its own meaning and essence. Humanity is something special, according to his beliefs.
Existentialism is basically very unscientific and non rational, a theory that grows purely out of arts and letters and standing independently of religion and science. It belongs to the no man’s land of philosophy, as Russell called it, though he avoided existentialism totally in his History of Western Philosophy. Perhaps he was wise to do so? His analytic tradition in philosophy is a completely different animal from the speculative tradition: more aligned with science and realism, which leads you back to determinism again. Maybe this perspective is more sane than the hyperbole of freedom and responsibility: more logical and consistent. The most convincing point of view will be consistent. And maybe the Cartesian approach was wrongheaded from the beginning? So that the absurdists didn’t know what they were talking about. Life is not absurd to a logical person, someone grounded in reality and in the laws of physics: in nature.