Lady Parthia did not have any problem with the concept of people trading necessary goods among themselves. She even welcomed it, understanding this was a vital necessity.
What she did have beef with was the concept of people in between- the middlemen, the merchants,
She saw these people facilitating this trade as little more than leeches who worked to only inflate the price of goods and make lives difficult.
Hence her next question to Alexander naturally became- "Then why don't the people who need the goods do it themselves? One of them needs grains, the other needs plows. It is easy! Why not trade it among themselves? Why need merchants?"
And reasoning,
"If they did it themselves, they would not have to rely on the greedy peddlers. They could even keep prices low at both ends and still make a bigger profit."
