Death of a Species
What would happen if you woke up tomorrow and discovered that the only males left in the world were cisgender1 men, and the only females left in the world were transgender2 women? What would happen to the human species?
What would happen is that our species would eventually die out. It would be the end of civilization.
Our species would eventually die out because humans are animals that propagate via sexual reproduction, and transgender women, regardless of how they identify or appear to the world, are still, biologically speaking, males.
Human sexual reproduction requires the fusion of two types of gametes. Male gametes (sperm), and female gametes (eggs).3
In our well-intentioned attempts to treat everyone equally, this distinction is often lost.