I seem to recall that when I was in college religious and philosophical discussions were fairly common, especially after a few beers. But it has been a long time since I have had such a live discussion. Here are some thoughts on why it is difficult.
First of all, it seems like nowadays the subject matter of social talk is extremely limited. In fact I can summarize what is allowed in a single phrase: personal activities. You are allowed to describe things you have done, or things that people you know have done. But even this is limited to brief descriptions of each item, before it is required to change people, or at least change subjects. So basically it amounts to reportage, with no extended discussion, and certainly no argument or opposition. So no science, no philosophy, and, above all, no religion. I am allowed to mention that I am writing a book, and to say the title and give a sentence or two about the subject matter, but then the discussion must change.
Now I can imagine a situation in which some people might wish to have a religions discussion with me. But who would this be? It would be evangelical Christians who want to convert me. Now I wouldn't really mind having a discussion with them, but I think it is pretty unlikely that I would end up converting them instead. Perhaps in another post I'll discuss what I think it is that strengthens and preserves the faith of an extemist.
So is there any chance to have a religious discussion with a moderate? It seems like you need some excuse to bring up the subject. Even in a one-on-one context in which the social rules do not preclude such a discussion, most religious moderates are not really interested in a religious discussion. They would have to be drawn in somehow. But I have an idea. If I say that I have just finished writing a book, and the subject is god and space aliens, then that might actually sound interesting enough to discuss further. I have found that it doesn't work in groups, but I can imagine it working in a small group. Now of course I would have to find someone who isn't already an atheist, and who I'm not afraid of offending. This may be the null set.
So you can see why writing a book on this subject is a lot easier than actually getting to have a live discussion. I have, however written the book as though I were having such a discussion. The downside is that I have to provide both sides of the argument myself, and most likely I am not being fair to the other side.
Perhaps next time the jehovah's witnesses come to my door I should invite them in.