>It's perfectly rational to want to buy twice as much flour if it's the same price it normally is, but not be willing to pay extra for the organic flour.
Knowingly putting pesticides in your body never seems rational to me, even if it saves some money. But if they were going to do that anyway, then sure, your point stands.
Organic products use pesticides, it's just that they often use older pesticide technologies or supplement the use of pesticides with other techniques for repelling pests. Most organic pesticides are no more healthy nor environmentally friendly than modern synthetic pesticides (maybe this wasn't true when DDT was popular, but these days it is).
For most Americans, they will eventually use their normal brand of flour, so buying extra is essentially no extra cost. (Time-value of money over, say, 6 months means that we're talking about a 1% difference here.) It's a cheap hedge against supply disruptions. But that's not very likely to happen. The organic brand is often at least 20% more expensive, making the calculus not worthwhile.
Put another way, if you expect flour prices to rise 10%, you should buy as much flour as you will use before it goes bad at today's prices, and 0 organic flour at a 20% premium.