“The real voyage of discovery consists not in seeking new landscapes but in having new eyes.” - Marcel Proust
I tend to like to write narratives and stories instead of long philosophical treatises (after all I'm a sociologist, not a philosopher), but I'll attempt to outline my thought process in which I stopped believing in god and a god-made religion.
It basically goes like this: We have no empirical evidence for god- all we have is a bunch of stories written down around 3000 years ago that clearly violate our modern knowledge of how the world works. So how could I believe these specific stories, when not only is there no independent empirical evidence for any of these stories happening prior to a certain time period (around the second temple), but those stories clearly violate scientific laws of nature and would be laughable if told today? Why are they any less laughable for having been written down 3000 years ago, when people had much less of an understanding of how the world works and so of course attributed all sorts of thing to "god"?
And if there is a god, why is Judaism the right religion? Every religion says THEY are the right religion, so what makes judaism more right than any other religion?
The more I thought about it, the more the idea of a personal god who cares about religious rituals just didn't make sense- why would god care if I ate a piece of bacon? What possible reason could an all knowing omnipotent being have for requiring these obscure rituals? If there was a god, and god was good, wouldn't it be more important for people to treat their fellow human beings nicely vs. following a bunch of obscure rituals while acting like assholes, which I found to be common among the jewish community? If god was so into these rituals, and those rituals were more important than how you acted towards your fellow humans, then he must be very petty. And if god is so petty, why should I follow god?
I eventually came to believe that no person can know what the hell 'god' wants if there is one, there is no evidence at all for god existing, and even if there is a god, the best bet is to just be a nice person and treat people well, rather than follow any specific religious rituals. Eden's wager if you will. Or like the quote from Kurt Vonnegut I have on my sidebar- "Live so that you can say to god on judgment day "I was a very good person, even though I did not believe in you." I started reading more about humanism, and realized humanist ideas were much more in line with my personal beliefs about life and how people should behave.
A big influence on my thought processes was Emile Durkheim's book The elementary forms of religious life which I read for my classical soc theory class my first semester of grad school. I loved his ideas so much that the cat I got at the end of my first year of grad school is actually named after him (his name is Durkheim).
Durkheim (the sociologist, not the cat) was also an OTDer, who lived in late 19th century France- his dad was a Rabbi. He argues in his book that religious rituals were a way of increasing group solidarity in the ancient world, designating things as sacred or profane and therefore designating people and objects and behaviors as "us versus them." This served an evolutionary purpose in that designating things as "us versus them" increased solidarity among the "us," and therefore increased safety in the ancient world. He also argues that an important function of religious beliefs is to give the believer strength and motivation to keep going in the face of adversity, and that in order to gain this benefit, religious people must constantly engage in rituals in order to renew that feeling of strength and motivation they get from religion.
The more I peered behind the curtain of jewish religious rituals and thought more and more about what some "latent functions" (underlying purposes) of those rituals may be, as I used this new Durkheimian framework to understand my upbringing, the more I became convinced that religion was man made, and that while the purposes of these rituals are beneficial to many people in contemporary society, to a non believer like myself they do not carry the same benefits.
I do believe religion serves an important purpose in society that has an evolutionary purpose- it still encourages group solidarity, which results in dense social networks willing to give social support, which therefore increases the probability of survival and reproduction. Some religious rituals - the niddah laws for instance, and modern prohibitions against birth control- increase the probability of reproduction directly.
Other benefits such as social support are still present in religion, but not necessary to survival the way they used to be. As any orthodox jew knows, if you run into an orthodox jew anywhere in the world they will probably be willing to help you out and invite you over for shabbas. You can get jobs and other social support though your jewish networks. These are all examples of the results of group solidarity.
I also think, as Durkheim points out, for some people the idea of a god, an afterlife where everything is just and assholes like JP get punished while good people get rewarded and you can meet up with your lost love ones- well it's a very nice dream. It would be great if it were true. It's especially important for people who are facing overwhelming adversity, which is why you always see tons of churches in poor neighborhoods. I think I get extra sad these days when people die (compared to how I felt when I still believed there was a god / olam habbah [afterlife]) because I just don't believe it's true.
On the other hand I know my parents draw a lot of comfort from that idea- for instance when my grandfather died, my mother told me that he kept talking to his dead wife on his death bed. To me that's just the result of someone with alzheimers hopped up on morphine and in the process of dying, and of course talking to the person who was his companion for over 60 years and had just died a couple of years earlier when his alzheimers was already starting to advance, but to my mom it was proof that my dead grandmother was in the room with them. I can see why that idea is very appealing, and I can see why it's a major aspect of many popular religions (A great movie about this point is "The Invention of Lying").
I just can't bring myself to believe in it personally, since ideas of the world to come seems to be based on pure speculation and desire for it to be true, with no empirical evidence. And since I don't believe in it, it doesn't give me comfort.