So you agree it can be an issue but the one who makes it an issue is the bad spouse, does that boil it down or am I missing something?
Let's get out of the blame game. I think the right question is this: what's the best way to have a loving marriage where we both feel loved and well-treated when we have strongly different feelings about one particular sexual practice?
We're talking about an activity that one of you finds thrilling and the other finds humiliating or distasteful or both. I'm guessing here when I try to describe your wife's reaction, because none of your posts have said anything about what this means to her emotionally, how it feels to her when you ask her to do this. Your posts aren't really asking how you can be loving and caring to your wife when you have different sexual tastes, they ask us to get on your wife's case if she doesn't do something many normal people would find demeaning. And your posts don't seem to focus on how you can make sex good for both of you.
You've already tried it, it's not working for her. She still tries it once a month or so, perhaps because of the pressure, perhaps to try to please you. Sex is a pretty emotional thing, I wonder how this kind of pressure to do something she really doesn't want to do will affect her feelings toward sex with you in other areas.
Frankly, in your posts it sounds like you're looking for some law that says you can force your wife to give you the thrills you would like and you don't have to care about her feelings. If you look at Scripture, I think you'll find laws like these:
You husbands in the same way, live with your wives in an understanding way, as with someone weaker, since she is a woman; and show her honor as a fellow heir of the grace of life, so that your prayers will not be hindered.
I'm not feeling a lot of understanding or honor in what you write when you discuss this issue with your wife.
Husbands, love your wives, just as Christ also loved the church and gave Himself up for her, so that He might sanctify her, having cleansed her by the washing of water with the word, that He might present to Himself the church in all her glory, having no spot or wrinkle or any such thing; but that she would be holy and blameless. So husbands ought also to love their own wives as their own bodies. He who loves his own wife loves himself; for no one ever hated his own flesh, but nourishes and cherishes it, just as Christ also does the church, because we are members of His body. FOR THIS REASON A MAN SHALL LEAVE HIS FATHER AND MOTHER AND SHALL BE JOINED TO HIS WIFE, AND THE TWO SHALL BECOME ONE FLESH. This mystery is great; but I am speaking with reference to Christ and the church. Nevertheless, each individual among you also is to love his own wife even as himself, and the wife must see to it that she respects her husband.
In your posts, you don't seem to be terribly concerned about nourishing and cherishing your wife, or treating her in a way that is holy and redeeming, loving her as your own body.
And you're not asking the question, "if there's something I'd like sexually that she finds demeaning, what's the best way for us to handle this as a couple", you're asking "if she doesn't want to lick my behind, isn't she being a bad spouse, withholding sex?" Your questions haven't been about how to improve your relationship, they have been about finding ways to put the blame on her or get her to do this for you.
Talk to your wife, tell her how important she is to her, how you don't want to put her in a situation where she's feeling demeaned or treated badly. Ask her how she feels about this, if she's felt under pressure. Really listen, give her plenty of time to talk without interrupting her, repeat back what you think you are hearing and make sure you've got it right, try to put yourself in her shoes. Ask her what would be really good for her sexually, what would make her feel loved and cherished and well treated. Ask her if anything you've been doing has hurt her, and be prepared to apologize. Be ready to learn and to care and to change. Get out of the blame game.
Jonathan