It's crime? From the linked Atlantic article:
"The book is deliberately and insistently inclusive—which means that it does not presume a 'normal' one-fertile-mommy-one-fertile-daddy household.
Indeed, the book doesn't even mention the word 'mommy' or 'daddy'. Instead, What Makes a Baby explains that 'Not all bodies have eggs in them. Some do, and some do not;' and that 'Not all bodies have sperm in them. Some do, and some do not.' Similarly, sex isn't so much tip-toed around as it is relegated to one unspecified option among many. 'When grown ups want to make a baby they need to get an egg from one body and sperm from another body. They also need a place where a baby can grow.'
Silverberg's goals here are very deliberate and (in the reader's guide) carefully spelled out. He wants to include all children, regardless of whether they have a mommy and daddy who had sex, or adopted them, or whether they have two mommies, or two daddies, or (as Silverberg mentioned in the guide) a trans daddy who gave birth to them, or any of a myriad of other possibilities. The book, then, tries not to impose one truth, but rather to open up possibilities and conversations."
It's quite threatening to some "traditional family" advocates when the reality that families exist that are not in the format of a married man and woman raising their biological offspring together. Undoubtedly, this book, recognizing the real life existence of real life other types of families, will be framed as an "attack" of sorts on "traditional families."
Again, I reference projection, and how considering the possibility of one's political opponents engaging in it can be rather insightful.
For, rarely do "traditional marriage" advocates, even when directly asked, have tangible solutions or alternatives to offer non-traditional families - particularly same-sex headed families - to address our needs and marginalization in a society that centers and privileges the heterosexual married family. It's as though in their ideal world, non-traditional families (and individuals) should either assimilate or not exist at all.
A Creepy Anti-Choice/Anti-Gay Thought Experiment
Catholic Leader Denies Reality
Is Extermination the End Goal?