Maybe not every moral truth can be exhausted by pure reasoning alone. The Christian always has the appeal to revelation as an epistemic modality for believing a particular moral truth. There are a lot of fine details though too. For example, I don't consider masturbating to mental images to be equivalent to masturbation to pornography. Many times, I take moral teaching in Christianity to have an esoteric and an exoteric component. On the exoteric side, we can construe the wrongness of masturbation as something having purely to do with just ends, or whatever. On the esoteric side, I often find (personally, anyway) that there are likely natural explanations, which if we were to dig deeply into the full psychological/physiological effects of masturbation, would prove to have detrimental consequences. In other words, morals like this one may say that the action is wrong because it is sexually nonproductive, but I also think that this level of reasoning betrays something more straightforward yet concealed - that Christian morals tend to optimize a person's psyche and experience of life (whether that be from physiological, psychological and/or social effects). For example, masturbation may cause you harms that you (a) are not aware of, or (b) which you are aware of but which you don't connect to masturbation conceptually. We might say these are downstream effects which the sciences have not yet (or refuse to) connected to masturbation. Perhaps these arise from the availability of masturbation and the convenience. That retaining semen and the effects this has on libido do something by way of conscious experience that has ripple effects that spread across your life. Or chronic masturbation effects neurotransmitter levels in the brain that alter your day-to-day consciousness. I genuinely believe that Christian virtues identify a way of being that tends to strike a balance across multiple dimensions of life (and desires) that achieves something like a dynamic stability or optimization. Perhaps masturbation once per week is more moral than 35 times per week. Or that entering into a relationship with a woman and having sex with her is more moral than either of these. Morals have ends, both for *this life* and the afterlife. I believe that. @PS