Most people who don't have kids (myself included) think they can still have valid opinions on child rearing. The more appropriate question to ask would be, "Have you tried this, and did it work?"

Until you have kids... most people who have kids think that your opinions aren't really valid.

I don't intend for that to sound mean. Sure, you can have your opinions, but there is so much that goes into raising a kid that you just can't know beforehand that you can't make an informed opinion. So, knowing if you have kids sets the level of expectations.

I think that it's fair to say that you can describe 'principles', but talking about putting those into practice is where people (such as myself), get touchy. This is especially true when you criticize someone else's choices.

Another way of putting it is this: In theory, there is no difference between theory in practice. In practice, there is.