The New York Times has an article this morning on Gwendolyn and Kendall Myers, who allegedly stole information and sent it to Cuba over the course of 20 years. Kendall Myers worked for the State Department (with a high level security clearance), and Gwendolyn Myers helped transfer stolen data to Cuban agents.
The strongest argument in support of the government’s case may have been made by the Myerses themselves. In the 40-page complaint they are quoted telling an undercover F.B.I. agent how much they admired Fidel Castro, how they sent secret dispatches to Havana over short-wave radio, dropped packages to handlers in shopping carts at local grocery stores, traveled across Latin America to meet with Cuban agents and used false documents to travel to Havana for an evening with Mr. Castro.
The Myerses might as well have been invented by conservatives concerned about left-wing activity in the United States government. The article reports that they held a romanticized view of the Cuban government, and they refused monetary compensation beyond what was needed to reimburse for equipment. Ms. Myers worked on the McGovern campaign, and Mr. Myers worked as an adjunct professor at SAIS. They were deeply disillusioned by American foreign policy. In 1979, shortly before Mr. Myers took his position at the State Department, their farm in South Dakota was raided by police and several marijuana plants were seized.
The key thing to remember is that intelligence sold to foreigners doesn't stay in the country that bought it. Every intelligence organization has ties to other organizations, and shares information (especially valuable information) accordingly. Similarly, foreign intelligence communities suffer from lapses and penetration just like our own; even if Cuba had wanted to keep secrets from the Soviets, it's unclear how successful they would have been. This is to say that espionage cannot be judged harmless based on the notion that the spying country is innocuous. Information, as they say, wants to be free, and when it gets free it tends to stay free.
Moreover, there really isn't any such thing as harmless data. Every bit of intelligence collected by a foreign organization contributes a piece to the puzzle and can lead to revelations about agents, methods, and the success of various operations. It's unclear precisely what the Myer's stole or who saw it, but the consequences may have been serious. This is why espionage is a serious crime, whether the information is sent to Britain, France, Israel, or, for crying out loud, Cuba.