There is nothng wrong with relating personal experience or saying 'what my health visitor told me'.
There is everything wrong with presenting this as advice for others or as if it is a statement of fact.
That's why replies to these experiences can sound a bit tetchy!!
There is plenty of decent evidence that eating well does not help a mother produce more milk and no evidence that it should. 'Natural selection' is no argument at all, fastasleep - in fact, you could argue the opposite way: the human beings who can produce plenty of breastmilk even in times of scarcity (which most of the human race has had to live with for most of our existence on earth) are likely to survive the best. Nature tends to look after the next generation, too (lots of examples of this, not always feeding related).
Experience also tells the same story: except in times of severe restriction of food, mothers produce sufficient breastmilk.
The way we tend to breastfeed in western society - feeding about 8-10 times a day tops, with babies sleeping and resting outside their mother's arms - is simply not good for milk production. Many mothers do manage a supply despite this, of course - shows how adaptable the human body is.
Gina Ford's theory of expressing in order to have enough milk when the baby really needs it, is just crackers. For some women, expressing twice a day more than the baby feeds/needs is a recipe for over-supply that can make them feel very uncomfortable. It's just not necessary.