I'm sorry you are accusing people of being dumb and not understanding supply and demand, but he's right.
His quote that you are getting worked up over:
en.wikipedia.org
Let's follow both curves.
SUPPLY:
As the price increases, people want to supply more, because they can sell it for more.
DEMAND:
As price decreases, their demand for the good decreases, because its ratio of value: cost worsens.
We can probably stop right there, since it's elementary that increasing price reduces demand.
However if you want to explore the concept further, there's the elasticity of demand:
en.wikipedia.org
The elasticity of demand translates the change in demand with the change in price.
Something that is
highly elastic responds substantially to changes in price. Something where the change in demand is less responsive to a change in price is called
inelastic.
Examples of highly elastic items include restaurant meals, luxury goods, etc. These are things people forgo easily when the price is too high.
Examples of highly inelastic items include basic food staples, medicine, etc. These are items that, even if the price increases, people are somewhat required to purchase.
TLDR:
You should probably not shout how people are stupid when you are wrong.