ESR claims 'silent trade' is universal objective ethics. It is in fact merely prudence.
The cannon-toting Europeans could take all the goods off the beach and run. The cost is not getting future trades. Even cannibal half-savages don't cooperate with defectors. If the trader thinks before they act, they realize they end up richer if they continue to trade.
ESR also overlooks this:
The silent trade works because the sailors have supremacy at sea, the villagers supremacy on land.Though that's not exactly true either. The EV of cannon-invasion is the gains from invasion minus the risk of costs from invasion. Meaning war is profitable compared to trade only if war is cheap, even if victory is guaranteed. At that time, the cannon-boats would have had to pay for war themselves, rather than having e.g. you pay for it. Further, they'd then have to mine or find the gold themselves, rather than paying natives to do it for them. Ergo, trade.