Your first point is debatable. The uniqueness is a scientific fact. If that were true that they are separate living entities then the little zygotes should pop on out and start living. But they are not separate living entities. It is life completely dependent on the host for everything, and lets face is some of the hosts should never have babies.
A newborn is equally helpless & dependent on its parents for its survival. Given the planet's population count, it's logical that a large majority of fertilized eggs are born. And yes, with distinct DNA, they are separate entities which are forming. Just because they can't survive outside the womb yet, does not detract from this.