BDSM is a lifestyle but not a religion. The reason I say this (as well as all the other excellent points made above) is because BDSM changes on a time scale a lot quicker than any religion. BDSM practise and ethics are always undergoing changes as we evaluate and revise what we do. Many religions get stuck into ruts of dogma which limit thier ability to change with the times.

Of course, this is not to say that we do not have dogma of our own and that there are many who are stuck in their ways. However, we are still more prepared to assess our beliefs and codes than some religions are and make significant changes to them.