What I see being overlooked in this discussion is what the role of a parent is/should be.
To me a parent is there to guide their children through their stages of development to help them be best prepared for adult life on their own.
Figuring out how one fits into the world is a challenging part of growing up, and a parent plays a role in helping their child navigate this. This doesn't meant they have to tell them how, or determine how they do it... but there is a role the parent should be fulfilling here.
What these parents are doing, and my here are advocating is leaving the child to navigate a confusing and often hostile environment with no help or guidance.
Rcade uses the example that a child who has never seen a pool until the age of 6 can still learn to swim. What this doesn't account for, is by that time many if not most of their peers will already be adept at swimming. Doing cannonballs, diving for rings, etc.... While this child will be unexposed, just learning, most likely feeling like an excluded outsider. You're basically advocating that we place the child near a pool as an infant, and let them self determine what happens. Rather than taking them into the pool, exposing them to water, teaching them a dog paddle, etc...
We are supposed to be here to raise the next generation, not just let them wander off on their own. Helping them figure out who they are and how they fit into the world is just another aspect of this.