I know I'm a finite and fallible human being who doesn't have a monopoly on truth.
This. Why do non parents give so much advice to parents? What do you have to gain? Parents at best just nod politely to your clueless advice and at worst make fun of you.
Even when people think they are right and have the soundness of the NAP backing up their positions, it helps to understand that even the libertarian ideology serves a limited purpose, mainly that of providing an individual with an ethical code. In an imperfect world of fallible people, there will be 'imperfect' actions, and people should be free to find (market) solutions in their lives with as much accordance towards the philosophy of liberty as possible. In not advocating a specific form of active governance of human action, temperance is the implied virtue of a wise individual seeking harmony.
Just because someone does not have any children doesn't mean they would be a bad parent, or a poor advice giver. BTW, why would someone with a genuine concern for the welfare of a child be dissuaded by ridicule from parents? Granted, it could be an ineffective communication exchange, but it does not imply fault one way or the other.
To simplify the argument: Some people are over-zealous in spreading their opinions. Temperance is a virtue, but only one virtue. Parents do not have absolute control of their children as they grow into individuals, ethically or realistically.