the response that I am talking about comes from the life force itself. Nature in the raw, heteros are genetically programmed by nature to find intercourse with the opposite sex exciting and very pleasurable.

Even without contraception procreation is, at best, a random by-product of heterosexual intercourse which in terms of incidence is overwhelmingly about pleasure. Do the math - how many kids do we have in a lifetime? How many times do we fuck? It's barely significant. Human beings find sex pleasurable. It's what sex is - the instinctive animal urge to PURE UNADULTERATED PLEASURE, be it heterosexual or homosexual - this is why we do it. It is always exciting & pleasurable. It is all about the life force and capacity to ORGASM which is, after all, PERFECTLY NATURAL REGARDLESS. If the extremely occasional incidence of sexual intercourse results in procreation, then the species is assured survival; otherwise Nature in the Raw does not discriminate.