This was originally the quick and dirty skeleton
of a writeup
. I never got around to any other proscriptions to apply my overzealous logic circuits to, and given the negative response, it's better that way.
I'm happy to listen to calm, rational non-religious counter-arguments and calm, rational religious counter-arguments. Shouting about the Bible as the literal Word of God only makes my ears hurt, though, and just doesn't convince me that I'm wrong. If "God said so" was a good enough argument to me, I wouldn't be writing this node, would I? I'd like to point out that these are just my ideas on what logical or social rationales might underlie assorted religious proscriptions, and as my ideas they reflect my personal, agnostic point of view (and a certain, mildly acidic humor, some of which is pointed at myself too). YMMV.
Jews keeping Kosher
I'm sure you've all heard about how important it is to cook pork properly, lest you get trichinosis. Well...
During the period of time that the Jews were busy writing the Torah, they didn't have refridgerators or anything else to keep meat (especially pork) from going bad, and didn't have really good controls on cooking (fires don't have temperature knobs). So, in the interests of not having any more Jews (a relatively small group to begin with) die from food poisoning, a number of sanitary rules appeared to prevent such culinary diasters, even if they didn't know what it was. Having them be the Word of God made sure that everyone followed them (so you wouldn't get trichinosis from visiting a pork-loving friend).
Update: stand/alone/bitch kindly /msg'd me to let me know that this has been disproven. I'm looking for some data to back this up. So far, one interesting point has come up: pigs are difficult to keep in the desert because they require a lot of water. Learn something new every day.
Lillith as the Breath-Stealer
Perhaps you might have heard of that murderer of children, SIDS (Sudden Infant Death Syndrome)? Well, nobody (as far as I know) really knows what causes it - they might as well just say "the baby died and we don't know why." Well ...
Back in ancient times (through the heyday of Greek mythology even), if something inexplicable occurred, people were most likely to attribute them to the powers of the gods, rather than, say, the laws of physics. So, if your baby suddenly died, wouldn't you rather say that some evil figure of legend was responsible than yourself? Call her, say, the Breath-Stealer.
Christian prohibitions against birth control, homosexuality, abortion, and suicide
So, you're one of the 12 Apostles and you really dig all this stuff that Jesus Christ told you and you want to spread it around and let everyone know about it and get everyone saved. There's two big options: conversion, and procreation. Well ...
Conversion's ok. Unless you get a good charismatic leader again or convert someone in power, it's going to be slow going, though. And they might backslide. So your best bet, really, is procreation. It's even got the added bonus that you can bring the children up inside the faith and they'll probably become believers. At that point, anything which inhibits procreation is a Bad Thing, and should be proscribed. Birth control and abortion are pretty straight forward. And homosexuality? Well, how many homosexuals can have children on their own?
And of course, you can't have your faithful killing themselves off, so you say that suicides will go straight to some awful place. Call it Hell.
As an exercise for the student: how does this apply to proscriptions against onanism?
Women being "unclean"
There are many proscriptions regarding menstruating women. These include: she must live apart while bleeding; a marriage performed during her period is not valid; her husband may not touch her for 7 days after she ceases to bleed. The first stems from fear, the second two have physical roots.
Menstruation was a source of power in matriarchal societies. It was a sign of fertility. When Judaism went with a male-dominated monotheism, it was imperative to eliminate this source of female power. So, women had to be shunned from society when they were menstruating. (If you think this wouldn't generate shame in women, there are several psychology experiments you should investigate. Start with Milgram.)
As for the second proscription, consider that women were supposed to be virgins before they were married, and that proof of their virginity must be given (usually in the form of stains on the sheet from breaking the hymen). If a woman were bleeding, this could not be verified. The third proscription has the side effect of having the woman be in her most fertile time of the month, making sex for procreation purposes only (see above re: birth control and homosexuality).