perhaps economic necessity shaped the moral code of the Tanakh (aka the Old Testament) -- that pastoral societies have a need for maximum reproductive output from each person... hence mandatory marriage, polygamy, prohibitions on homosexuality and masturbation, and so on.

the generally accepted explanation, as far as i have learned over the years from various texts, professors, and even the priests at the catholic high school i attended, for the strictures of the early Israelites' society is that there was a dire need to differentiate themselves from the numerous tribes that were surrounding them, especially considering that there never existed a clear-cut Israelite ethnic group- these were people who were converts and deserters from other tribes and nations. in order to cement their identity, everything from dietary to sexual regulations were put in place- the hittites eat animals with cloven hooves, so we no longer eat cloven-hoofed animals, and so on, as a physically-qualifiable measure to protect their nascent identity as a separate culture.

this does, in a way, support your new ideas. insofar as taking on these laws was an act of demarcation between Us and Them, it was surely politically motivated. as a matter of fact, the seeds were here sown for the countless rivalries that continue to burn through the middle east- "oh, those israelites are too good to fuck and eat shellfish, who do they think they are- who do they think WE are?". while not that simple at all, it is from this surface of simple cultural differences that years-worth of deep-seated issues have unfurled.