My response to the Quora question:
“I admit to having a visceral response to the answers heretofore provided. When a person answers to two masters, dividing her/his loyalties, no master is served. This is no more true than in intelligence.
We are not talking about two agencies sharing information, as with Five Eyes. The question concerns a single individual employed by an intelligence agency. When such a person sells the host country’s secret to a foreign agency—any foreign agency—that person is a double agent, guilty of espionage.
Jonathan Pollard worked as a civilian analyst for the Office of Naval Intelligence, during which time he passed suitcases filled with secrets to America’s close ally, Israel, in exchange for thousands of dollars. He was sentenced to life in prison but was paroled in November 2015 after having spent 30 years behind bars.”