All girls have to be willing and mentally stable and not under the influence if you're going to have degrading sex - or any sex - and not feel like a rapist.
Why is it undignified? I don't think it is. And a lot of us do things that others might not consider to be dignified, for a paycheck. Some people wipe asses, others clean streets, others lie to get criminals off and get really huge paychecks, others market lethal cigarettes to kids and adults, well... they have sex, sometimes degrading sex. What's the damn difference. We're all selling something.
Each to their own.
I am a little disappointed fox. When a person feels the need to question whether their actions make them feel like a rapist, maybe it's a sign that's telling them something. It seems to me that you are condoning any action as long as the other person is "OK with it," regardless of the notion that a seeming respect for the person would entail you to do no harm. This also is a little bit too close to the rational of an abuser for my taste, that always justifies their harmful behavior as not their own but the will of the person they are perpetrating it on. how many times have we heard "she asked for it"?
There's a difference between kinky and degrading. You can have wild sex and still be respectful of a person, not treat them like shit. The bottom line is that any person that willfully abuses or conflates abuse as a sign of affection and seeks it out is not mentally stable, as you put it.
Also, as I've recently stated, we all have choices. Maybe some of us don't have many of them in the matter of what we need to do to make a living. But the people that dish out the paychecks, as in the people that make the profit and promote services have the choice of not running a business that is degrading and harmful to their workers, and they should be held accountable for it.
I'm not trying to diss on you here. Hope that you can understand my criticism as constructive debate.