BDSM is neither a religion nor a cult in my opinion.

I think there is ample evidence already in this thread to support the fact that BDSM is not a religion, most importantly the fact that it goes against the basic definition of religion.

As for the more extreme claim that BDSM is a cult, I strongly disagree. Firstly, cults often try to indoctrinate minors, which BDSM strictly avoids with age limits. Secondly, BDSM offers a lot of personal freedom to both Doms and subs with regards to even such fundamental things about what BDSM is. You wouldn't see Scientologists offering these choices about the meaning of Scientology for instance.

Thirdly, while each group or event has its own rules, these are often a matter of practicality, and vary wildly from event to event even within the same organization. The dress code for a munch for instance is radically different than the dress code for a play party and each is often dictated by the location of the event, and other practical considerations. This is a far cry from some sort of uniform.