The question was what is the reproductive system for. For as in ultimate purpose. For as in why did God (or evolution, if you prefer) give it to us. Why is it there?
It must be admitted by anyone who isn't barking mad that the *purpose* of the sexual organs is to reproduce the species.
so what do the lips, the mouth, the tongue have to do with ‘the reproductive system’??? nothing, but, apparently, in almost NO human society do they NOT have something to do with sex
Ah, but you make the leap from organ systems to actual organs. It's patently obvious certain organs can be used for a dual purpose--in males, for example, the urethra is used by both the excretory and reproductive systems. The mouth is used for digestion and respiration.
But is the digestive system ever used for respiration? No. Is the excretory system ever used for reproduction? No. They may share pathways, but they do not share purpose.
And I am not a materialist. So I would never say that sex is purely biological. In human beings it is spiritual as well.
Finally, to answer your question, no, the "use" of non-generative organs during sex is not sinful so long as the generative nature of the act is preserved.
“The question was what is the reproductive system for. For as in ultimate purpose.”
that’s the whole point
reproduction is an “ultimate purpose”
yet, beyond ‘reproduction’ sexual intercourse has been recognized to serve an ‘ultimate purpose’ of its own, in the relationship of the human couple, as a couple
whether or not reproduction occurs, whether or not reproduction is intended, whether or not reproduction is desired
and, in that purpose, throughout human history, it - the sexual relationship of the couple - has not been, in it physical practices, limited to the mere functionality of the biological requirements for reproduction
therefore, to define the sexual life that exists, physically, between the human couple, beyond the mere bilogical requirements for reproduction, as immoral unless reproduction is intended is a non-sequiter - the idea that it must is a theological fiction outside of human life, from time immemorial