> It's not superior.
Why is a non-exclusionary alternative not superior? If it conveys the same meaning without being exclusionary, why is it not better? It's only not superior if you think being exclusionary isn't a quality, or utterly disregard its importance.
> Out of almost half a billion English speakers, probably a very tiny percentage 'highly educated' people would ever even think that this is a topic someone might have an opinion about.
Argumentum ad populum. Even so, you seem to be projecting: how do you know people actually agree with you?
> Everyone else, from small children on up, would just explain to you that a 'bad guy' can be a boy or a girl.
Would they? Have you gone out and asked them?
'tis true, 'guy' is sometimes rather generic, so they might say so. It's not the best example. But until you actually go out and ask, we don't really know. Err on the side of caution.
(I should note that while 'guy' may be generic in some contexts, this is only because maleness is considered generic in our culture, so it would still be problematic in that case.)
> This reminds me of the people who try to claim (hopefully tongue in cheek?) that history somehow encodes maleness because it has the word 'his' in it.
It's either tongue-in-cheek or a misunderstanding of etymology. Using his-story can be a political statement about how history as we chronicle it has largely focussed on men's achievements to the exclusion of others', though.