People simply ignore that point. Posterity means DESCENDANTS, not people who just happened to be born here.
The meaning of Article II is written right there in the Preamble. "To Secure the Blessings of Liberty for Ourselves and our POSTERITY" Meaning our children and our descendants.
The Constitution was ordained and established to secure the blessings of liberty to our children, their children, and their children's children, and so on and on.
Article II codifies it.
-PJ