How can I differentiate a photography club from an art club?
I've been thinking about your question and here's my take on it. Photography is a type of art, however, photography also has a close relationship with science. Specifically light and optics. If you can't convince them that photography isn't distinguished enough from art, perhaps you could convince them that photography is science.
Here are some differences between art and photography that may help you.
Photography is science based (light and optics). Art is different. Not knowing the chemical composition of your paint won't prohibit you from making a great painting.
Art is subjective while photography is (at least partially) objective. What I mean by this is that there are rules and guidelines (i.e. rule of thirds) about photography that make photos not just a matter of opinion. Photos can be technically correct or incorrect.
That's all I've got. I really hope you are successful in starting your club. Good Luck!
What to do during a club based on religious discussions and debate?
I personally find debates fun and that's what I would expect out of a religion club (I'm an atheist). A good idea for less serious yet more thought provoking debating is to pick an issue and have people choose sides, then each side has to defend the opposite position that they chose, obviously at next week's meeting to have time to prepare. Those kinds of things can be very interesting and force people to think about other points of view. You could do a whole variety of topics with that idea and possibly get some interesting results.
You could potentially get members or maybe teachers who would be interested to do short lectures on a religious topic that interests them which could spark discussion (virgin birth, original sin, magnets if you have Mormons, whatever).
You know basically every religion related topic will be a serious debate starter (just look at the questions asked here), so I say let the debates happen. It would probably be helpful if you had a teacher as a moderate to keep things under control, that or you would need a clear leader for discussion who people would be willing to listen to.