This is a false equivalency. Can you name an item acquisition game that implemented trade but didn't balance around it, thus it was truly optional?
Price fixers, scammers, flippers, the Mathil Effect, inherently reducing item value due to other players getting more value from the same item(Emblems during Legion league are best example of this, but Uber key frags are a current one). I'm sure I could list more if I took the time. There's tons of minuses to a game that includes trade. I'm going to assume "and balances around the assumption that it's being used", because otherwise why bother?