Professor Koji Murata likes to ask his political science students a tough policy question: Is it ever proper for a government to lie to its constituents?
Class opinions vary, but Murata, a scholar of international security issues at Doshisha University in Kyoto, has his own view.
"I think it's OK to lie to the public for the public good," he said. "As long as what you say is not contrary to national intent, really important secrets must be kept."
The philosophical question has gained urgency in the wake of revelations here of a decades-old secret pact between Tokyo and Washington that allowed nuclear-armed U.S. vessels to dock at Japanese ports, despite laws here against it.
For 40 years, the government denied the existence of the 1969 agreement between President Nixon and Prime Minister Eisaku Sato, the architect of Japan's post-World War II pacifism and staunch antinuclear policies.
Successive Japanese administrations were wary of a public outcry in a nation that suffered two devastating nuclear attacks 65 years ago.
Days after he took office in September, however, Prime Minister Yukio Hatoyama assigned a panel of government officials and historians to investigate Japan's role in the agreement.
Since the end of the Cold War, nuclear-armed U.S. ships have stopped docking in Japan, officials say.
The findings, due out this month, could further complicate a tense standoff between Hatoyama and the Obama administration over Japan's calls for the removal of a controversial U.S. military presence on the southern island of Okinawa.
"This revelation makes maintaining a stable alliance even more challenging," said Carl Baker, director of programs at the Center for Strategic and International Studies' Pacific Forum.
Many Japanese applauded Hatoyama's effort to create a more open government but said they felt betrayed by leaders who had publicly railed against nuclear arms, only to secretly acquiesce to the demands of a powerful nation.
Some are particularly incensed that the deal was struck with the United States, which dropped the atomic bombs on Nagasaki and Hiroshima at the end of World War II, killing as many as 220,000 people.
Bloggers have ridiculed Sato's 1974 Nobel Peace Prize, calling Japan's longest-serving postwar prime minister a hypocrite.
As she boarded a train home to Tokyo recently, Aikiko Shiono said she felt betrayed by the pact and the government stonewalling.
"Japan is the only country on Earth to suffer the devastation of a nuclear bomb," said Shiono, who works for a political think tank. "We shouldn't allow nuclear weapons to enter our country. We have to keep advocating to the world how Nagasaki and Hiroshima were a tragedy. To do otherwise is an insult to the victims."
Sitting a few seats ahead, Shiono's father said he disagreed.
"There are things the government has to hide from us," said Kenji Kobori, 60. "They have to make some tough decisions. Some of those have to remain secret."
The agreement, which scholars say violates a Japanese law forbidding nuclear weapons from being made, possessed or stored on this country's territory, was made public by American officials after the U.S. military stopped sending nuclear-armed ships to Japan in 1991.
Despite the U.S. government's admission, Japanese leaders continued to deny that there was such a pact.
"They did not exist," then-Prime Minister Taro Aso said during a nationally televised news conference last year in response to a reporter's query about the pact and revealing documents.
The deal restoring Okinawa to Japanese sovereignty reportedly hinged, in its secret portions, on the U.S. retaining the right to dock nuclear warships at the base in case of emergency.
Security analysts were divided over Japan's handling of the secret agreement.
"I think it's always useful for citizens to know what their government is up to, even decades after the fact," said Jerome Cohen, a legal expert at the New York University School of Law. "We learn what to do for the future from our mistakes of the past."
Baker said the issue was more complex than learning a history lesson.
"Is it useful to bring out information about this pact now? These kinds of things are never useful when it comes to national security."
He said the revelation could play a role as Tokyo and Washington hammer out a deal on a new location for a controversial U.S. Marine Corps air station on Okinawa.
"This is another thorn to deal with, on top of everything else between the two nations," Baker said. "Part of me says that, like it or not, history has to be revealed. But how far do you take it? At what point do you trade off national security for full disclosure? Should we start disclosing past CIA operations? We know they existed.
"It's a tough issue. There's just no easy answer."
One former Japanese government official said that such secrets are kept by all nations.
"It isn't just Japan," said the former ambassador, who requested anonymity because of the sensitivity of the issue.
The ambassador said Sato was empowered to enter into such a deal to help Japan secure the return of Okinawa. But he said the deal should have been made public years ago.
"It was a lie, and they should have corrected it after the Cold War ended and the U.S. nuclear ships stopped coming," he said.
Murata, the political science professor, says the debate will continue in his classes as to how Japan should treat U.S. nuclear vessels in the future.
"It was a betrayal and it went on for decades," he said. "Now the government has finally come clean. But the question remains: With an unstable North Korea, how do we assist our closest ally without a secret pact?"