Genuine, Authentic Desire
The basic question posed by Twisty is whether any women every really like giving fellatio to a man*. I think we can separate this into two questions: is a woman's desire to give fellatio to a man ever genuine, and if it's genuine is it ever authentic. A genuine desire, as I'm using the term here, means one that is experienced as subjectively real by the desirer -- it really runs through the desire circuits of her brain. On the one hand, un-genuine desire to give fellatio to a man is common -- many women report being pressured, by individual lovers or by societal norms, to give fellatio that they don't really enjoy. On the other hand, though a few people who have embraced a very crude form of radical feminism and irresponsibly universalized their own experience may deny it, widespread genuine desire to fellate men does in fact exist. It's impossible to explain away the large amount of testimonial evidence from women who do experience real, direct pleasure from the act.
Unfortunately, a lot of sex-pos people stop with the establishment of the genuineness of desire, while radfems want to probe the authenticity of desire -- leading to a lot of talking past one another. An authentic desire is one that is "really yours," not a result of social conditioning. The usual way of describing this is to ask whether you'd still desire something if there were no patriarchy. An inauthentic desire can still be perfectly genuine -- patriarchy (or whatever social conditioning system) has the ability to make you actually like doing the things it wants you to do, not just to externally coerce you into doing them. I think there are problems with this model of people having real pre-social desires with cultural conditioning layered on top of them. But we can reformulate it in a way that preserves the essence of the radfem concern while recognizing that all desires are created in a social context. The question of authenticity is the question of the origin of a genuine desire -- is it produced by a force that we can approve of, or is it produced by a force we would like to do away with? I'll keep the somewhat unsatisfactory label "authentic" for desires resulting from approvable forces. Understanding the origins of one's desires in this way can be helpful in deciding whether and how how to reform one's own desires, or one's participation in desire-creating forces, with the ultimate goal of producing more consistently satisfiable desire packages.
So where does the desire to give fellatio to men arise from? We can see the radfems and sex-pos as each giving a plausible hypothesis. The radfem hypothesis is that the desire for fellatio is cultivated by patriarchal socio-cultural systems as a way to get women to serve men's pleasure and mark their own submission. This hypothesis has a great deal of face validity. We can document the cultural messages and direct compulsion along these lines in both women's and men's magazines, in the statements of many men to their buddies and their lovers, and in porn. This hypothesis clearly accounts for the prevalence of non-genuine desire to give fellatio, so it's hardly a stretch to imagine it cultivating genuine desires as well -- though many sex-pos people tend to conflate genuineness with authenticity, assuming that the authenticity of a desire can be validated by their own subjective feelings.
But the sex-pos side has a good hypothesis as well. There are a variety of authentic reasons one might desire to give fellatio to a man, such as the pure physical pleasure of mouth-to-genital contact or the enjoyment of having him in a vulnerable position (think of the damage teeth could do) and directing his experience. Many radfems are so fixated on the patriarchal pro-fellatio narrative that they dismiss alternative narratives as necessarily rationalizations. But in fact they are quite plausible, internally consistent, and not at odds with any objective facts about the act (after all, these reasons apply just as well in the case of cunnilingus, where there's no patriarchal pro-cunnilingus forces that we might just be rationalizing).
We must also flip things around and do a parallel analysis of the desire not to give fellatio to men. Here, radfems are quick to point to plenty of reasons why one might not be keen to give fellatio -- the taste, discomfort from performing the action, etc. (hence, of course, the term "funk-filled bratwurst"). The sex-pos side will happily recognize these reasons, and defend the right of any woman to refuse to give fellatio on this basis. Unfortunately, some radfems are quick to universalize these reasons -- fellatio is objectively disgusting to anyone, therefore authentic reasons for doing it must not exist, therefore only inauthentic reasons could explain the existence of genuine desire to give fellatio. But there are also plenty of inauthentic reasons one might not want to give fellatio to a man. For example, the strength of the "receiving fellatio as an act of domination" discourse can poison the whole act for someone.
So both the radfem and sex-pos side have hypotheses with strong face validity. Moreover, I don't think we can give the automatic burden of proof to one side or the other -- we don't have to disprove all authentic hypotheses before we can entertain an inauthentic one, or vice-versa. This leaves us the difficult task of sorting out, for any individual person or for women as a whole what the balance between the two causes is (and therefore what proportion of fellatio desire is authentic). Unfortunately, nobody in this debate seems to have a very good idea of what kind of evidence would settle this question.
* The question of giving fellatio to a trans woman or non-binary person is largely ignored in the debate, mostly because most radfems don't accept the validity of these people's existence.