"I don't belong to SBL, partly because I haven't got around to it, but partly because I wasn't really sure how much 'use' it would be to me. I guess the name 'Biblical Literature' speaks to me of literature that made it into the Christian canon (and possibly the deuterocanonical books). My only real contact has been through a few papers from SBL conference proceedings and through the SBL fonts email list.
Logic suggests that an organisation that is working on such a wide range of fonts can't be devoted solely to Christian canonical and deuterocanonical material, but I think the title is unfortunate for those who are working either outside the canon or from outside a faith perspective. I've visited the website several times and looked at what the benefits of membership are and decided that they're probably not all that great for me. As a Christian minister working on Nag Hammadi texts, I obviously don't find a particularly large group of colleagues within my own denomination, but the SBL website doesn't actually convince me that I'd find many more within its ranks.
This is quite possibly a very unfair jugdment of SBL, but I suspect that this is possibly the kind of thing SBL is working against. And archaelologists are wary of theologians and biblical scholars.
I couldn't work out for several years why one of the archaelogists at my university avoided me even though we shared several common interests, until we needed to work together on a particular project. After that, he decided that I wasn't going to shove the Bible down his throat at every turn. We now spar gently in public forums when his rampant atheism gets too much for me, and get on quite well in private, but I could understand why people like him would vote against joining SBL."