I guess I'm not seeing the special category that an anime cat girl sits in. Is there some kind of sex implication I'm just not aware of? Linux has a penguin, FreeBSD has a devil(!), OpenBSD has a blowfish, Go has the weird Gopher thing, Gnome has a foot...

Wikipedia suggests that there's an association with queer and trans youth, is that what's meant to make the cock-and-balls comparison work? But it also says it has a history back to 17th century Japan...

If it were just the imagery I don't think this would be such a huge flashpoint relative to something like tux or octocat (the github mascot).

Because it's really about the type of people (they think) watch anime, and their inability to separate this preconception from reality.