The reference is to a children’s picture book, And Tango Makes Three, about two penguins who adopt an egg and raise the hatchling. It just happens that the two penguins are male.
It’s a true animal story, which I’m a sucker for. I don’t like it though because it anthropomorphizes the penguins, which is fine for fictional stories but not for non-fiction (imho).
That’s not why it’s so often banned. I’ll let you figure that one out.
Books are meant to be free!