Coker, Catherine. 2013. "Earth 616, Earth 1610, Earth 3490—Wait, What Universe Is This Again? The Creation and Evolution of the Avengers and Captain America/Iron Man Fandom." In "Appropriating, Interpreting, and Transforming Comic Books," edited by Matthew J. Costello, special issue, Transformative Works and Cultures, no. 13. https://doi.org/10.3983/twc.2013.0439.
Many scholars have attempted to explain why women read and write slash stories. For the purposes of this study, I'm not interested in recapitulating this research, since it has been so heavily documented elsewhere, but I would like to note the work of Joanna Russ on the topic. "If you ask 'Why two males?'" she said, "I think the answer is that of eighteenth-century grammarians to questions about the masculine-preferred pronoun: 'Because it is more noble.'…No one [can] imagine a man and woman having the same multiplex, worthy, androgynous relationship, or the same completely intimate commitment" (1985, 84).
As frustrating as it seems some 30 years later, this attitude definitely persists. Further, the most specific element—(gender) equality—actually grounds the Captain America/Iron Man or the Steve/Tony ship. As written by fans of that ship, their relationship is the only possible true partnership (figure 1).
Steve is an idealist with a practical streak, while Tony is an "ends justify the means" pragmatist with an idealistic streak. This leads to frequent clashes between the two of them over methods and tactics, but at [sic] also means that the two of them balance one another remarkably well. Tony challenges Steve, forces him to rethink his assumptions and defend his ethical position—and Steve needs that. Without someone to question him, to treat him as a friend and comrade instead of "Captain America: Living Legend," he'd still be stuck in 1945. For Tony, Steve's friendship and faith in him provides both a sanity check that keeps him from straying too far into supervillain territory, and the support that allows Tony to keep on fighting the good fight, to keep on trying to live up to and be worthy of that faith. Tony has declared on multiple occasions that he thinks Steve is a better man than he is (he even goes so far as to tell Steve that he's perfect), and that Steve's faith in him is the one thing that allows him to still have faith in himself. (elspethdixon 2008)