Ari - I get somewhat get what you are saying, however I like to dominate and part of that is the use of the submissive for sex, and I AM taking advantage of the submissive by doing so - that is part of the dominating. Besides the spanking or binding or clamping or exhibiting that one might do - there could be for some the using, or even moreso the sharing for use by others in any way that the Dom determines, and that is very much a part of dominating. And if humiliating is also part of the Doms thing, then how can he be "protective" of the "fragile" psyche of the sub, when what he wants to do is exploit it.
curiouser and curiouser -
Submissives tend to break themselves out into different types. There are slaves, fuck-toys, service submissives, etc. A service submissive is generally speaking not in it for sex and may not even be into pain or humiliation. He/she is there only to serve (i.e. cleaning your apartment, running errands, etc). Someone being a submissive does not mean that they are going to be into all aspects of BDSM just as someone being a Dom does not denote that they are into humiliation.
The backbone of the Dominant/Submissive interaction beyond play is to take a submissive and mold her into what best serves him/her. This does not necessarily mean turning a service submissive into fuck-toy or vice versa, but rather taking what's already there and making it into something better. Humiliation can simply be a tool used to do just that. A "good" Dominant is not going to humiliate a submissive who finds such activities abusive. The interaction is not supposed to be "exploitive", but rather one of mutual enjoyment. A submissive may find humiliation useful in focusing them on their Dominant's pleasure. Another may just find it a turn-on. While another looks at it as a punishment for an infraction. By respecting those limits (and perhaps pushing them at times) a Dominant could be seen as protecting a sub. A dominant who loans out a submissive who is not ready for such an activity, could end up without a submissive or the submissive could end up being...well there are enough horror stories that abound in the "scene" of emotionally and mentally damaged subs.
You really can't take advantage of someone who wants to be taken advantage of. And taking advantage of someone is not Dominanting. In order for the whole dom/sub interaction to even happen to begin with...the sub has to give up control. So, it kind of moots the whole thing. However, once again giving up control does not mean doing away with their respective limits.
It's really about finding the right partner. If you're into sex and humiliation then you find a submissive who's into those things as well (and they're out there).