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Last month, I was in Sweden meeting with think tank and government officials. The main purpose of the visit was to discuss EU-U.S. policies toward Iran, especially the effectiveness of the international sanctions seeking to change Tehran’s nuclear policies. But some of my Swedish interlocutors, like other Europeans, also raised the issue of the ineffectiveness of the arms sanctions towards China as a reason for their skepticism regarding the Iranian sanctions.

Their arguments should be looked at, but first it’s important to offer a little background on the issue. The killing of many unarmed protesters involved in the Tiananmen Square demonstrations and elsewhere in China provoked international outrage and led many countries to adopt sanctions against Beijing,...