The morality, to me, is ultimately simple.

I would never do anything to another person that would damage them or that they would not consent to.

Certain groups -- children, mentally handicapped, animals -- do not have the power to consent.

Beyond this, it is important to understand that pain is NOT the opposite of pleasure, but is in fact very closely related, those being the only two extreme sensations available to humanity. One can inflict pain or discomfort to produce pleasure, and doing so is a way of showing love. Nor is this uncommon -- who hasn't playfully bitten their partner's neck, or revelled in a forbidden tryst in a car's awkward seat? We are not a subgroup per se, with unique tastes or desires; being in the scene is simply a matter of extremism.