Free Will, Evil, Culpability

As has been previously discussed, the concept of human Free Will often seems less a product of Psychological observation than a device to exonerate a good and omnipotent God from the existence of Evil.  For example, Descartes advocates a version of the Theological thesis, by asserting that error and sin are derived from an abuse of Free Will i e. from choosing what is not clearly and distinctly perceived.  Now, on the one hand, in the Fourth Meditation, he presents Free Will as as absolute as divine Free Will, but, on the other, in the same paragraph, he discerns a difference of degree between them, in terms of "knowledge" and "power".  So, regardless of what he means by those latter two, the qualification implies that Free Will, in general, is a variable quantity, dependent on other factors.  If so, then it is not as absolute a factor in human experience as Descartes posits it to be, in which case culpability for Evil is not as easily assignable to humans as he presents it to be.  Thus, while that nuanced variability, that he himself allows for, might better explain concrete motivation, e. g. impulsive behavior, it undermines his Theological presuppositions more than he seems to recognize.  In contrast, Aristotle and Spinoza each offers an example of a concept of Volition not constrained by those presuppositions.