As I mentioned in my January 30, 2016 post, Grace Jantzen in Foundations of Violence makes a compelling case that Diotima is a fictional figure. She does not, however, adequately distinguish her from the poetizing female figures Parmenides and Boethius portray as instructing them in their respective works. If nothing else, the quality of the poetry of Parmenides and Boethius betrays the influence of a very real woman: Sappho.
By contrast, Plato essentially portrays Diotima as the personification of his philosophy–his metaphysics–and it is hard to believe there was such an ancient Greek woman. Although the term ‘metaphysics’ derives from a neologism coined in Greek centuries after Plato and Aristotle lived, its meaning (‘beyond’ (meta) the ‘natural,’ or ‘embodied’ world (physics)) appropriately characterizes what Diotima and hence Plato’s philosophy is all about. A key passage is where she characterizes the most intense love as “gazing at and being with” the beloved, without even the need to “eat or drink.” That leads her to ask rhetorically whether it would not be best to gaze at what is not “infected” by flesh and blood (Symposium (211 d-e)).
Compared to many issues related to ancient history, it is relatively easy to identify not just where and when misogyny began to contaminate theology, but the person primarily responsible for it: Plato, who lived in Athens in the late fifth and early fourth centuries BCE. Although today Plato is not thought of as a theologian, in antiquity theology was not just one discipline among many, but rather was synonymous with philosophy as an overarching system of thought to which all else was subordinated. Conceived of in this way theology was comprised of a variety of interrelated theories that today ostensibly appear to be discrete disciplines, including biology and psychology.
There is thus little question but that the exclusion of women not just from theology but from literate culture generally up until the 20th century can to a great degree be attributed to Plato. In one dialogue he categorizes women as a subaltern species of humanity that has yet to evolve to the level of being attained by men. Consistent, in an odious way, with that biological theory, is Plato’s view of female psychology as being such that it should be against the law for women to establish private religious shrines and related rituals since they derive the inspiration for doing so from dreams, apparently incapable of the ‘serious thought’ he deemed necessary for such matters. Given that context it is hardly surprising that in all his ‘dialogues’ there is not one female participant.