It’s a definition. When something doesn’t match the definition, it doesn’t meant the definition is wrong it means it’s wrong to call that thing that term.
Greed is, by definition, irrational. But greed vs generosity is independent of capitalism.
If you want to see what “capitalism” is, learn what a definition is and how that relates to reality.
If there are people who truly have no choice, then you don’t have a free market and you don’t have capitalism. However, I will say that I was homeless and during that time my choices were constrained but didn’t disappear. I stopped being homeless because I made the right choices while homeless. This “having no choice” thing is simply not true.