Behavioral economics have repeatedly showed that humans are consistently irrational when it comes to buying and selling stuff.

Modeling humans as rational agents simplifies the economic reasoning and the equation a lot so it's not entirely worthless, but we must always keep in mind that this model is very far from the reality even if it's sometimes useful.

That points more to the will of rationalizing people behavior through simple models than how much rational people can be.

How rational is the endeavor of creating rational models? At some point, people act on a mix of empirical and acculturated faiths. What's valuable, worthless or taboo depends on each unique situation.