The first reason that I don't engage in discussions of religious beliefs is that I don't see any benefit in it. I don't expect to learn anything, and I don't expect my opinions to be persuasive to my conversation partner (more on that later), so I just don't have any motivation to participate. To make it worse, I doubt that it matters whether I believe in God or not.
The second reason that I avoid these conversations is that there is always a risk that the other person will be upset by what I say, either getting insulted, or defensive, or possibly even having their faith shaken. It's hard to politely tell someone that they appear to have built their life on wishful thinking, and that I have no interest in joining them in their delusions.
Still, this is one of those topics that is often worth broaching just as a "get to know you" type of thing, so I should figure out how to talk about it... and I'm gonna have to review how I got to where I am.
I used to be interested in religion. I grew up nominally Christian, though mainly I was a fairly passive theist. Really, all I wanted from God was some signs as to what I should do with my life. When I realized that I wasn't going to get these signs (around age 16) I had my major break with theism. I continued to explore theism for several years, with books and friends, but by my mid-twenties was pretty much done with it.
Discussions of theism often get started with a sort of "natural theology". Of course, this is the most logical entry point for a discussion when a theist is talking with someone whose beliefs they don't understand. I regularly encounter a few basic theist arguments -- what we might call "first mover", "intelligent design", and "magnificent universe" -- that I find completely unconvincing. It's kinda hard to produce anything but a blank stare when someone dishes me these lines. It seems that I can either arrogantly point out their logical error (e.g. assuming that a powerful intelligence is behind anything of interest) or just play stupid and say "I don't understand what you mean" until they give up in frustration. Neither is appealing.
The times that I have tried to engage with the above ideas, I have completely failed to connect with the monotheists whom I am speaking with. When I follow those lines of thoughts, I end up at some sort of pantheism, and with an exasperated conversation partner. The other problem is that I have only encountered one phenomenon that suggested intelligent design, and that is the interaction of the human brain with the compounds within psilocybin mushrooms. There are a variety of reasons that I refrain from bringing up that experience, depending on whom I'm speaking with.
If we get out of natural theology and deal instead with revelations, then I am forced to confront the credibility of whatever religious tradition inspires my partner. This is just asking for trouble. Once I get around the general problems with revelation, then we have to deal with the well documented history of lies and threats that separates us from the supposed revelation. I really don't want to go there.
The final problem that I have when discussing religion is that I don't have a nice label for my beliefs, and I don't belong to any organized school of thought. Others are content to identify as a "Christian" or a "Jew", despite the great variety of beliefs that fall under those labels. I could point to a variety of philosophical traditions, of which I only have passing knowledge. So I could say that I've liked what I've read about Epicurus' philosophy. I like
So here I am, left without much to say when my friends talk about their deepest thoughts. Oh well.