Please feel free to E-mail me with your own comments on this issue or on anything else included in my Philosophy of Life section. This is the second of a four-part reply.
Sex certainly feels just as good to unmarried partners as it does to married couples.
Also, your argument isn't reflective of the reproductive patterns of practically every animal species on the planet. Females of most species go into estrus and become receptive normally only from once to a few times each year. Copulation with their mates must occur during these rare periods or there will be no offspring produced that year. There is no pleasure aspect at all that drives this instinct, it is purely a matter of species survival. Even if those species engaged in constant copulation throughout the entire year, there would be no increase in the number of offspring.