"For example, it's my theory that the taboo on homosexuality in some societies began with inheritence issues. In societies where land was left to the oldest son, what if he was an only son and he was homosexual? Then if he had no children, it complicated inheritence and the land staying in the father's direct line of heirs." -
In cultures influenced by Abrahamic religions, the law and the church established sodomy as a transgression against divine law or a crime against nature. The anti homosexuality taboo was born among the ancient Hebrews. It first appears in the sayings of reformers in Hellenistic Judaism as they attacked the sexual practices of neighboring fertility Cults.
The ancient Hebrews developed sexual attitudes drastically different from the rest of the world. According to some authorities, the sex-negative orientation developed about 700 BC, following the Babylonian Exile; before this, the Hebrews, like other asiatic peoples, had also allowed homosexuality, including male prostitution as a part of temple worship.
Homosexuality in China, known as the pleasures of the bitten peach, the cut sleeve, or the southern custom, has been recorded since approximately 600 BCE.
Homosexuality in Japan, variously known as shudo or nanshoku, has been documented for over one thousand years and had some connections to the Buddhist monastic life and the samurai tradition. This same-sex love culture gave rise to strong traditions of painting and literature documenting and celebrating such relationships.
In Ancient Greece, regard of male homosexuality such documents depict a world in which relationships with women and relationships with youths were the essential foundation of a normal man's love life. Same-sex relationships were a social institution variously constructed over time and from one city to another.
Firsthand accounts from European explorers detail not only homosexuality among the Native Americans, but transsexuality, as well. Transsexuals in the Americas were known as "two-spirits," the idea being that they had a spirit within them for each gender.
So, no inheritance issues have nothing to do with it. Abrahamic religions, that's another story.
Addressing your third or fourth paragraph:
"If you take god(s) out of the picture, many religious laws cover common sense and ethics. Or they address practicalities...." -
The Code of Hammurabi (dating back to about 1772 BC), is the longest surviving text from the Old Babylonian period. The code has been seen as an early example of a fundamental law regulating a government, a primitive constitution.
The Mosuo of southern China. None of the Mosuo have any kind of marriage. They have concept of tisese, which other people in China translate as "walking marriage," but which literally translates as "goes back and forth." If a woman wants a child, or just wants some entertainment, she invites a man to practice tisese with her. He comes by, and they have sex. But she kicks him out in the morning, and there's never any talk of their living together.
A tisese can be totally secret, with no public acknowledgement of the relationship at all. Couples handle these liaisons the way we did in college: When a man comes over, the woman hangs his hat on a hook outside her door, and though people may not know the gentleman caller's identity, they all know not to disturb the pair. The tisese may also be more public, with the sort of gift-giving you associate with a wedding. But either way, the man never moves in with the woman. There's no commitment. And when the woman gives birth, the man isn't a parent, isn't part of her household and plays no part in the child's upbringing.
The man stays at his own home and helps raise his sister's children instead. In each family, the woman acts as the head, and children have no fathers but each has various uncles.
According to one strain of logic, this lets each man raise a child that he knows is his relative. When you marry a woman, you can never be quite sure if the children she bears have any of your genes. But when you raise your sister's children, you know those kids have some of your family's blood in them.
Religion still is the root of all evil.
Ismael