What about pain though? This part of BDSM seems purely physical and not related to humiliation.
Surely the administration of pain itself can be considered humiliating - an adult person inflicting this on another adult - especially in a discipline/punishment situation. It's not humiliating to be bent over a knee awaiting and getting a bare bottomed spanking?

But I agree when it's done purely for pleasure on both sides, it's more difficult to see it as humiliating.

After a while, what BDSMers do seems so 'normal'!