It's not really any more likely than a longtime stage actor beginning to believe that he actually IS Hamlet after playing the role for twenty years.
In this way, a master plays the role of casting director before the first denigrating words are out of his mouth- he has to pick the right slave for the part, rather than just throwing her on stage and seeing how she reacts. In my case, my slave must share my views not only about the eroticism of the act, but in the reasons behind that eroticism. A slave sharp enough to see those reasons and discuss them (as they are described in the above articles) will certainly never fall prey to the phenomenon you describe.
When needed, protection or aftercare can take the form of reassurances, (whispered or emphatic), or periods of counterbalancing exhaltation where the slave is complimented at length and put on a pedestal to reward her for her obedience, willingness and beauty. In addition, simple reminders that the exercise is rooted in untruth will probably do the trick. Sometimes it is necessary to really delve into the psychology behind the act and remind a submissive that the reason such interaction is satisfying is that she is falling from a great height, but only temporarily. A master should be interested in the descent of angels, who subsequent to the act, will rise back up to the clouds. It takes a cruel and irresponsible man to be aroused by the rutting of pigs, who rather than sacrificing their self-esteem, have none to begin with.
If aftercare is frequently needed (at length) and the submissive begins to express many doubts, then it's time for the master to modify his behaviour and discuss new limits with his slave- that is the responsible thing to do. As for a slave becoming convinced that degrading statements are true, or truly feeling worthless afterwards, it is as I said above. I find it very implausible unless the master has grossly misjudged his slave, and chosen one who doesn't understand that the eroticism comes from untruth and dichotomy. If it starts to happen and negatively impact his slave, the only course of action is to accept his mistake and attempt to repair the relationship.
If this happened to me, I'd me more disappointed in myself for misjudging my submissive than I would in the submissive.
Again, the odds of that happening are low unless a master attempts to browbeat a slave with these techniques when she lacks the mental sophistication or experience to understand that the eroticism comes from falsehood, not truth.
If a master brings about these poor results in his sub, it's a miscalculation on the part of the master and he is the one culpable. He should have the strength of character to own up to the fact that he abused (though unintentionally) the trust that she placed in him by taking it too far- and then modify his behaviour.
- FS