Ben Myers graciously notified me of this excerpt from Stringfellow: http://cruciality.wordpress.com/2010/08/02/stringfellow-on-masturbation-sex-and-the-search-for-self/.
The thoughts I shared with him I will share with you:
"I confess that I was not too impressed by Stringfellow's observations. Indeed, he already has taken the presupposition that the act of masturbation requires a sexual fantasy. As he basically admits, his theological qualms are not with masturbation itself but with sexual fantasy, and the reader is left to assume on faith that masturbation is the efficient cause of the above and thus guilty by association. This will not do. One might as well condemn push-ups due to the fact that many do them as a stimulus for a subsequent arousal and aberrant sexual experience."
Efficient cause does not mean primal cause.