I assume when I meet parents with an only child over the age of five they did not like the experience of having the first child and decided not to have any more
Why would you assume they don't like their first child?
Well. Either they didn't want to have any more children or the child disturbed the household balance.
That is not something that you can assume. There are many reasons why a family only has one child.
Ok so.... You just don't get it. I'm trying to be reasonable.
What you are saying is not reasonable at all. There is no reason to speculate why family only has one child. Keep thoughts like that to yourself.