Concupiscence, Sex, and Self

I have not studied sexual ethics much, nevertheless, I have some thoughts on the subject. 

Scripture is decisive that lust, fornication, adultery, homosexuality and beastiality are morally prohibited. They are sins or morally wrong acts. Moreover, we can deduce from good and necessary consequences with Scripture pornography and abortion is morally prohibited. So if masturbation includes any of the aforementioned sins it would not be morally permissible. In the absence of such sins (e.g. lust, pornography) is masturbation sinful? Insofar as masturbation is discussed in Christian sexual ethics it’s moral status is underdetermined from Scripture.  Since there are no clear and conclusive proof texts on the matter. Perhaps we can theorize further on the issue. Thomistic tradition would argue from natural law that masturbation is sinful. It goes against the very design of genitals and sex itself. They may possibly argue the purpose of genitals is for sex between a married man and woman. Moreover, sex is designed primarily for procreation and secondarily pleasure. The design priority is given to procreation not pleasure; but, even if this wasn’t the case, it is necessarily between two people. This seems to preclude self-gratification from stimulating his/her genitalia. But perhaps natural law is bogus. Or, simply the purpose of sex has different conditions. Suppose sex has three conditions of procreation, pleasure and intimacy with the overarching purpose to glorify God. It seems a person may argue the target is not missed if at least one of the conditions is met. But some may argue from counterexamples that procreation and pleasure are merely sufficient conditions but not necessary conditions. Intimacy is then identified as the likely necessary condition for sex. But then one wonders what is the difference between sex, hugging or spooning on such an analysis. It seems to trivializes sex or makes it equal to hugging or spooning. Perhaps just revise the conditions to be merely ideals. If so, then sex can be without procreation, pleasure or intimacy yet aim to glorify God. 

Or think about sex as being essentially an other-centered act where pleasure is a bonus. A man gives himself to his wife for her pleasure yet as a bonus gets pleasure himself. Conversely, masturbation is self-centered thus goes against the nature of sex. But of course, one may press the question, is this version of sex altruism actually egotism at some level? 

Let’s explore a different angle. Does masturbation cause a person to grow in the fruits of the Spirit? Self-control and/or the love demonstrated by self-sacrifice? Does such an act exemplify Christ’s character? 

Does masturbation have the appearance or perception of evil? Is it associated with sin? Will the world see you as the same or any different from them in this action? Will such an action tarnish your witness and testimony of Christ to the world if that action is public knowledge?