Forms of Venery
The Word
The English words "venery" and "veneration" both derive from the Roman goddess Venus, but their meanings are entirely different, denoting respectively the activity she represented and the honour she received.
Natural and Unnatural Venery
The psychic union that is at the heart of the developmental mandate, and therefore necessary for the full development of any self, involves an asymmetry of genders so depends for its full functioning on an underlying asymmetry of sexes.
Forms of venery that support such asymmetrical union are natural; other forms are unnatural.
Natural Venery
The Forms
The male-dominance instinct is flexible in the forms it takes.
Our chimp 1st-cousins form loose bonds or none (polygynandry).
Our gorilla 2nd-cousins form harem-bonds (polygyny).
Our gibbon 3rd-cousins form pair-bonds (henogyny).
No apes form reverse harems (polyandry), which would be incompatible with male dominance.
Harlotry (Fornication)
Unbonded mating is especially harmful. However casual they may want the liaison to be, it inevitably tends to create a bond, subsequent suppressing of which coarsens erotic sensibility instead of nurturing it.
"He who joins himself to a harlot is one body. For, as it is written, The two shall become one flesh."
Paul of Tarsus, 1st Corinthians 6:16. "Harlotry" in this sense, what used to be called "fornication", includes all unbonded venery. Paul interprets Genesis 2 to the effect that "becoming one flesh" is an outcome, not of the couple's intentions, but of the mating as such. Hence his claim that the union occurs even in the most casual liaison.
Henogyny
To vary from our 1st and 2nd cousins in favour of our 3rd cousins by practising henogyny is wise because it optimises the complementarity of genders that is essential to human social ripening.
1. The psychical union that I have mentioned as the distinctively human refinement of the simian mating bond is generally best served by henogyny.
2. The above point becomes sharper if we remember that man's proper ultimate goal is a union between God's masculinity and our relative femininity. God of course is capable of simultaneous union with any number of people, but I suppose a man might have difficulty on this point with more than one wife.
3. The propriety of a man enjoying "more than his fair share" is obviously doubtful.
I usually assume henogyny, referring to a man's "wife". "Wives" would be more accurate, using the familiar grammatical convention that plural form allows for singular cases, but could give the impression that I advocate routine polygyny, and endlessly denying this would be tedious.
Polygyny
Polygyny is unlikely to be wise except in exceptional cases.
If a missing wife (presumed dead or otherwise) turns up after her husband has taken another wife he should treat both as his wives; these cases may be unusual, but if either of them is accepted it establishes that in principle we have a casuistry not an absolute prohibition. (This enables us to avoid tricky questions of whether to presume death. No need to decide; hope for the best and fear the worst!)
One New Covenant Book writer, in urging (1 Tim 3:2) that a polygynist should not become an episkopos ("elder", leader), seems to imply only that a polygynous arrangement has some relevant drawbacks, not that entering it is always wrong. Perhaps he regarded taking aditional wives after joining the ekklesia as wrong, but the New Covenant Book is never explicit on that, and the nature of the drawback is not given; it may have been no more than an avoidance of stumbling-blocks, a concession to the sensibilities of Jewish reborns.
Unnatural Venery
Sodomy and Tribadry
A homoerotic (or a "bisexual") inclination is learned not innate, even if some humans are innately more prone than others to be led astray thus, and hinders healthy development by blocking (or distracting from) natural venery, so those who have learned such an inclination should try to unlearn it, not reinforce it by homosexual venery.
Apes form no same-sex quasi-mating bonds. Some animals sometimes do, but usually only in response to a shortage of potential mates, as in prison-sodomy; a homoerotic orientation in animals seems rare.
Solitary Venery
Solitary venery (sometimes metonymically called "masturbation") may be useful in psychic emergencies, just as an analgesic poison may be useful in organic emergencies.
Incest
Venery between a pair who were in the same family when one of them was an infant is usually unwise because it risks disrupting the healthy development of social interactions. As explained by Talcott Parsons in Family, Socialization and Interaction Process (1956) (2.8), eroticality is so closely connected with the surviving structures of infantile dependency that venery with "any of the figures of the original drama" would push the whole personality towards reversion. This applies only to the nuclear family, who usually happen to be 1st-degree relatives. 2nd-degree relatives (first cousins) are likely to be entirely free of such complications.
Inbreeding tends to degenerate the stock, human or otherwise. This applies most strongly to 1st-degree relatives but also to a lesser degree in the 2nd degree and (with decreasing force) beyond.