In general, consent is not enough. Abuse is abuse whether the recipient consents or not. Afterall, the battered housewife who refuses to file charges and comes back to the abuser over and over again is indeed consenting to the abuse, and yes, that's abuse. Both physical and mental mistreatment can qualify as abuse.

I think, however, if the consenter is willing, it is never abuse. How do you define "truly hurts his sub" (or her sub) if that sub feels completed by it? Is compelled to it? Relishes it?

Now we can argue what it means to be "willing". But I think it is important in defining WIITWD.

PS. SSC, RACK and WIITWD (what is is that we do) are all terms created in the community to try to explain ourselves to those who don't, as an attempt to show consent and safety... so they'll stop bothering us. But it's no more or less safe and sane than contact football, racecar driving, skydiving, base jumping, stunting, "jackassing" or any number of hobbies the vanilla world participates in freely. It just happens to be sexual and that makes it a taboo and "somehow wrong" to them.