Religious Customs: Possible thinking behind them

Religion, the opium of masses isn't more potent in any other place then in India. The country might be second most populated, but certainly boasts the highest population of Gods. In-fact I can safely say that each of the Upnishads (one of the religious scripture of Hinduism) will have mention of more gods then all the gods that Greeks could have thought of. (Greeks would be the second most populous deity community). Ubiquity of God is what every religion preaches, but influential mid-century Indian followers went a step ahead and created ubiquity of places of worship. They were thinkers of tomorrow, so they could see that in future there would be chronic shortage of land hence the people per unit place of worship might not be sustainable, so they came up with new ideas. Associate certain trees with a God, so if you do not have a temple around, you can have your god equivalent banyan tree, or maybe catch a snake and feed him, and God would reciprocate with blessings. If you have river or mountain around, they are worth worshipping, so save flat areas for housing construction and make temples in same caves of mountains.
The “custom” creators had also foreseen the food shortage, and hence devised a method to cut down upon consumption through ingenious concept of “fasting”. Some would say that it works well for the digestive system etc., but for medical effectiveness of fasts it should be done once every month and a recovery regime have to be followed after it. Certainly fasting twice a year or for 3 days in an auspicious week or only during daytimes in a month, would do no good particularly when it is followed by hefty food. If you think that PETA is something that originated in modern times than you are duped by a gimmick. There was an earlier avatar of PETA which was more secretive then priory of Scion, and infiltrated in the team which was designing the religious customs every time. Though unlike present PETA movement, these ancient infiltrated had some personal penchants for certain animals, so someone who loved Cows, made it a holy animal and got all future generation of cow protected from a large chunk of masses while someone else made some other animal listed as "dirty" and hence got it protected from even larger chunk of humans. These people could not be regarded as true originators of PETA rather the person who first thought about holistic animal welfare and fought hard to protect them by strongest mode, religion should be the deserving founder. Since he/she didn't had a very strong influence so could get the clause of “eating animals” as forbidden, for only certain communities. He/She might have been successful for getting it for entire follower section had it been any other day as the day of discussion was the day when the “Rajinder dhaba” equivalent of that times had started their centre and had made their inagural delivery as free to these guys. Tasting the delicacy they thought that it would be utterly immoral if they keep entire future population aloof of such great experience hence complete ban was ruled out. But still post this event, Neanderthal man who ate raw animals, had offspring who would categorize touching a well spiced meat, as sin. The PETA lobbyists were strong, so they could not seek a complete ban on eating of animals through "custom" changes, but they did include some confusing clauses. These clauses made many present day humans to be totally unclear on the correct custom and they end up being “purely human” by not eating animals, on a particular day of a week just to be safe. So by and large the objective of those earliest PETA activists was partially successful. Rejection of complete ban had fallout as well. Few of these early PETA lobbyists defected from the mainstream religion and helped in establishing new religions, which had “no-killing” as guiding principle. However they could not get much people to switch loyalties from the older religions as by the time these lobbyist had become totally active, Rajinder express equivalent had infiltrated in much larger parts and addiction to well cooked chicken/meat was difficult to get out of.
Whatever might the present state of customs and following be, one thing is clear that there were far sighted and thinking individuals who conspired to create customs and thereby have contributed in lessening the vagaries.

P.S: I would be dishonest if I would say that I deny existence of God. Neither I am well read in religious scriptures, so many assertions might be ignorant opinions. I have better knowledge of one religion (the one to which I belong) so could cite more examples from that only