I think it is rather odd that people think bondage neccessarily equals SM. BDSM = Bondage Domination Sadism Masochism. These are different but sometimes overlapping. Cetainly, rope bondage can be entirely sensual. I'd highly recommend reading a thesis by a good friend of mine Sense & Shibari
I'd suggest more of you enjoy pain that realise it. Do you ever/enjoy biting, scratching, playful slaps during sex? Like hot and spicey food? Well, isn't that chemically induced pain? ;-) Pian kicks of pleasure giving endorphines, the body's natural opiate-like chemical.
IMHO, we all have relics of our more primitive past when less consensual sex was the norm. In my, anecdotal, experience the male pain threshold drops dramtically immediately after orgasm and many women get turned on by rough (consensual!) sex. I believe the reason for the drop off in male pain threshold is because he must not be deterred from his biological duty by female resistance, i.e. procreation, but once achieved Mother Nature turns the protective mechanism back on so to prevent damage and preserve him to impregnate the next. The female response to this resistance is increased lubrication etc. to facilitate the act. I'd be fascinated to see if this thoery could be verified by those more knowlegeable than myself.
As somebody who makes their living teaching and performing rope bondage, I suspect I might have a better insight than those who merely read about it. Feel free to Google my screen name but best not do it at work ;-)