1) The cultural norms issue, especially as it turns up in the anti-slash argument in Holmes and other historical fandoms: "But they wouldn't have done that! That was criminal/sinful/taboo back in those days!" It would be nice to get into some nuanced discussion of how people are influenced by their culture's sexual ideologies without necessarily obeying all the rules.

2) The nineteenth-century medicalization of homosexuality, especially since Watson is himself a doctor.