WASHINGTON—Most Americans seem to reject the U.S. trade embargo against Cuba. According to a Washington Post/ABC poll, 57 percent of Americans now oppose the policy. A survey by Bendixen & Associates shows that only 42 percent of Cuban-Americans continue to back it.

I have been conflicted on this issue for years. Until not long ago, I favored the embargo. As an advocate for free trade, I would normally have called such a measure an unacceptable restriction on the freedom of people to trade with whomever they pleased. But I thought that trading with a regime that had killed, jailed, exiled or muzzled countless of its citizens for decades was not a worthy objective, as it would also preserve that dictatorship. Any transaction with Cuba would also benefit the government. After all, the authorities were already skimming 20 percent of the remittances from Cuban-Americans and 90 percent of the salary paid to Cubans by non-American foreign investors.

Eventually, I admitted to myself that there was an intolerable inconsistency in my thinking. No democracy based on liberty should tell its citizens what country to visit or whom to trade with, regardless of the government under which they live. Even though the Castro brothers, Fidel and Raul, would obtain a political victory in the very short run, the embargo could no longer be justified.

But this is not the reasoning coming from the most vocal critics of U.S. sanctions these days. Many of them fail to even mention the fraud that is a system which bases its legitimacy on the renunciation of capitalism and at the same time implores capitalism to come to its rescue. There is also an endearing hypocrisy among those who decry the embargo but devote hardly any time to denouncing the island’s half-century tyranny under the Castros.

Another risible subterfuge attributes the catastrophe that is Cuba’s economy on Washington’s decision to cut off economic relations in 1962 after a wave of expropriations against American interests. The amnesiacs conveniently forget that in 1958, Cuba’s socioeconomic condition was similar to Spain’s and Portugal’s and the standard of living of its citizens was behind only those of Argentines and Uruguayans in Latin America. Many of the critics also seem to suffer what French writer Jean-Francois Revel used to call “moral hemiplegia”—a tendency to see fault only on one side of the political spectrum: I never heard Cuba’s champions complain about sanctions against right-wing dictatorships.

Sometimes, sanctions work, sometimes they don’t. A study by Gary Hufbauer, Jeffrey Schott, Kimberly Elliot and Barbara Oegg titled “Economic Sanctions Reconsidered” analyzes dozens of cases of sanctions since World War I. In about a third of them, they worked either because they helped to topple the regime (South Africa) or because they forced the dictator to make major concessions (Libya). Archbishop Desmond Tutu told me a few months ago in San Francisco that he was convinced that international sanctions were crucial in defeating apartheid in his home country. In the cases in which the embargo worked, the sanctions were applied by many countries and the affected regimes were already severely discredited or weakened.

In the cases in which sanctions have not worked—Saddam Hussein between 1990 and 2003, and North Korea today—the dictatorships were able to isolate themselves from the effects and concentrate them on the population. In some countries, a certain sense of pride helped defend the government against foreign sanctions—which is why the measures applied by the Soviet Union against Yugoslavia in 1948, China in 1960 and Albania in 1961 were largely useless.

In the case of Cuba, the Castro regime has been able to whip up a nationalist sentiment against the U.S. embargo. More significantly, it has managed to offset much of the effects over the years in large part because the Soviets subsidized the island for three decades, because the regime welcomed Canadian, Mexican and European capital after the collapse of the Berlin Wall, and because Venezuela is its new patron.

But these arguments against the U.S. embargo are mostly practical. Ultimately, the argument against the sanctions is a moral one. It is not acceptable for a government to abolish individual choice in matters of trade and travel. The only acceptable form of economic embargo is when citizens, not governments, decide not do business with a dictatorship, be that of Burma, Zimbabwe or Cuba.