I personally was shocked at myself, when I carefully responded to my sub's first request to hurt her, and she received the (mild to moderate) pain with excited whimpers, that I was extremely turned on. Was I / am I a sadist? Who can say: it is only in the context of a request or a desire that the pleasure on my part makes sense, so probably I am not. But the deep and profound mutuality of the experience astonished, delighted and educated me.