In order to provide further clarification, I want to address non-kosher unions in light of both the subject of arayot and of zera levatalah.
The pronouncement of the living G-d Himself regarding the Torah law dealing with all aspects of sexuality - and the ill consequences of transgressions in these matters - is clear and decisive (see Vayikra 18:24-30). The sexuality declared by G-d as being impure and abominable, to wit, all prohibited sexual unions (arayot) which are known are galui irvah (“the uncovering of nakedness”, implying on an exclusively physical relationship and spiritually frivolous) is summarily forbidden and it is verily a hindrance to the person’s ascension in kedusha. This also means that such nakedness should literally be covered. And as it is written, “When the yetzer hara grows stronger in man, it only does so through his immoral sexual conduct. All sins are connected to the ‘uncovering of nakedness’” (Zohar III:15b, Vayikra). This is true even is the person is considered in all other aspects of his life, as good, decent, and honored. However, the sexual unions called “knowledge” (which recognize the intimate physical-spiritual nature of the sexual union and its consequences) are not only approved, but allow great spiritual ascensions! The ones named galuei irvah are actual transgressions of spiritual law and bring upon people and the world great physical and spiritual devastation. As it is known, if the union through sexual intimacy is ‘abused and wasted’ (i.e., the act is not fulfilled leshem mitzva of procreation, as it is the case of a sanctified union), not only the potential of spiritual ascension fails to be realized, but the sexual energy in its ‘physical form’ (the involved fluids) vitalizes the chitzonim. This has the effect of subjugating the side of kedusha, chaz v’shalom. Moreover, the spiritual energy, vis-à-vis, the sexual energy used only for self-gratification becomes an instrument of disconnection and spiritual exile of the soul, assertively thrusting the person toward the domain of the klipot – where extraneous and impure spiritual elements negate the unity of G-d. This degradation implies on the loss of the person’s spiritual stature, for in only privileging the ‘animal aspect’ of an intimate union, he sustains only the level of an animal – below his complete experience of humanity.