What do authoritarian regimes like China, Libya, Russia, Vietnam, and a democracy like South Africa have in common? Their representatives voted against an arms embargo on Robert Mugabe’s regime in Zimbabwe during the recent U.N. Security Council meeting in New York. The South African vote, which will allow Mr. Mugabe’s generals to go on procuring weapons they need to complete the destruction of their domestic opponents, is as shocking as it is hypocritical. After all, the South African government claims to have a foreign policy with a strong moral dimension.

Nelson Mandela, the leader of the African National Congress who was later to become South Africa’s president, sketched out his country’s future foreign policy in the November/December 1993 issue of Foreign Affairs. It would, he wrote, recognize “that issues of human rights are central to international relations” and “that just and lasting solutions to the problems of humankind can only come through the promotion of democracy worldwide.”

It is quite shocking, therefore, that Mr. Mandela’s successor, Thabo Mbeki, decided to defend the Zimbabwean dictatorship at the United Nations by arguing that the U.N. Charter prohibits the United Nations from intervening in the U.N. member states’ domestic affairs. After all, the apartheid government used the same language while trying to keep the United Nations from condemning South African race laws and repression of organizations that included Mr. Mbeki’s ANC. The U.N. Security Council imposed an arms embargo on South Africa in 1977. Zimbabwe, alas, escaped similar fate last Friday.

In part because of the South African vote and behind-the-scenes diplomacy, Mr. Mugabe’s government will continue to acquire the weapons it needs to kill its opponents. All the while, South Africa’s foreign ministry claims to pursue a vision of “an African Continent, which is prosperous, peaceful, democratic, nonracial, nonsexist and united, and which contributes to a world that is just and equitable.” What are some of the reasons for this massive hypocrisy?

First, Pretoria wants South Africa to become Africa’s undisputed leader. Such leadership will magnify South Africa’s power and lead to a permanent seat on the U.N. Security Council. But uniting African countries around South Africa’s foreign policy objectives was never going to be easy. Therefore, Pretoria couched its goals in anti-Western rhetoric that paints Africa as a permanent victim and the West as an eternal oppressor. And who better to deliver Africa from under the Western yoke, but South Africa — preferably with a permanent seat on the U.N. Security Council.

Mr. Mugabe’s interpretation of the events that transformed Zimbabwe from one of Africa’s richest to one of Africa’s poorest countries fits the anti-Western narrative beautifully. Whereas most economists blame Zimbabwe’s collapse on Mr. Mugabe’s land grab and economic mismanagement, Mr. Mugabe blames it on a Western conspiracy spearheaded by Britain and America. To condemn Mr. Mugabe would amount to accepting that many of Africa’s problems are homemade. Mr. Mugabe must, therefore, remain beyond reproach.

Second, the Manichean dichotomy between the oppressor and the oppressed provides African countries, including South Africa, with an important advantage when negotiating with the West. The illusory state of permanent victimhood allows many African governments to demand aid, debt relief, and special treatment in trade negotiations, to name but a few, as a matter of right. Concomitantly, few of them feel bound to fulfill their reciprocal promises to the West.

Take, for example, the patently absurd conclusion of the G-8 summit in Gleneagles in 2005. In exchange for tens of billions of dollars in additional Western aid and across-the-board debt forgiveness, African governments have agreed to “better governance.” But better governance — be it defined in terms of greater rule of law or more sensible economic policies — should be Africa’s goal regardless of what the West does.

Even that commitment fell through, however. When the African Union had the opportunity to condemn the bloodshed in Zimbabwe and the subsequent theft of the June 27 presidential election by Robert Mugabe, the A.U. did next to nothing. It welcomed Mr. Mugabe to the A.U. summit in Cairo and put out a statement urging negotiated settlement of the Zimbabwean crisis. Once again, South Africa was central to derailing the efforts of those few African countries, like Botswana and Zambia, that wished to take a stand against Mr. Mugabe.

Of course, South African government can follow any foreign policy it likes. But, it cannot go on pretending to stand for freedom, democracy, and human rights, while protecting some of the world’s most odious regimes.

Mr. Tupy is a policy analyst at the Cato Institute’s Center for Global Liberty and Prosperity.