You may think you're a great father, but I don't know you. You're a stranger to me. I don't have any reason to believe you're any better than the last 20 people who tried to offer me contradictory unsolicited advice on how I should raise my children.

There is at this point no faster way to get in my bad books than to put your nose in my affairs and tell me how to raise my children when I didn't ask you to.

Maybe I misinterpreted your question. My answer was to a question more along the lines of "why do parents talk about parenting all the time?" If the person offering advice is being a dick about it (be it about parenting or anything else), then sure, it's inappropriate. But at the same time I remember when my first was born, I was pretty darn receptive to advice because _I had no idea what I was doing_. I'm less receptive now because half a decade in I think I have a decent handle on things, but I'm still not hostile about it -- I generally smile and nod and ignore (which, come to think of it, is what I do whenever anyone offers me advice I don't need).