Primarily it's an inappropriate use of the word incest. Some physical relationship were prohibited as incest (as contraception was an unknown concept) to prevent what is known as inbreeding depression, for reasons of progeny. So technically there was never a ban or prohibition for the emotional or psychological relationships.

But now the world is witnessing the out breeding depression, as we can see there are more children affected by variety of birth defects. So any relationship can be declared as incest.

Emotional incest is basically a hoax, causing hatred and rivalry within family.