SEOUL, South Korea — In the wake of the Charlie Hebdo killings, three million people marched in France to defend free speech.

But in South Korea — a staunch US ally — free speech is fraught, particularly for anyone caught praising the Kim Jong Un regime.

American citizen Shin Eun-mi, an author and classical singer, learned this the hard way after being deported from Seoul this month.

Her crime? Allegedly painting North Korea in a far better light than was comfortable for South Korea’s conservative government.

Following trips to North Korea from 2011 to 2013, Shin stood accused of making what authorities called supportive comments of the regime in a series of lectures.

Shin’s story is becoming ever-more common in a nation that has been turning back the dial on free speech.

Authorities targeted her under the 1948 National Security Act, a Cold War relic passed in the run-up to the devastating Korean War of 1950 to 1953. Following the North Korean invasion of the South, more than 2 million civilians died, and South Korea remained vigilant about the threat for the decades to come.

Effectively banning communism and “activities benefiting the enemy,” the law was historically wielded against actual North Korean sympathizers, along with legitimate opposition figures who challenged former dictators.

But the act, much to the chagrin of today’s leftists, has outlived South Korea’s rapid and remarkable shift to democracy. Ever since taking office in 2013, the government of President Park Geun-hye — the daughter of South Korea’s longest-serving dictator, Park Chung-hee — has deployed such legislation on a regular basis, crushing the nation’s dwindling hard left.

In December, the Constitutional Court disbanded the leftist United Progressive Party (UPP) for allegedly espousing an ideology of North Korean socialism. A key parliamentarian, Lee Seok-ki, was also imprisoned for 12 years for making statements on a recording, obtained by the country’s spy agency, that appeared to support an anti-government uprising in the event of a war.

Last Wednesday, South Korean authorities took the crackdown further, arresting far-left activist Hwang Sun for, like Shin, allegedly making comments sympathetic to North Korea. A hardcore North Korea supporter, Hwang garnered controversy when she gave birth to her baby in Pyongyang by cesarean section in 2005, and mourned the death of Kim Jong Il in 2011.

But the US citizen, Shin, whose legal name is Amy Chung, believes she is the victim of an anti-communist witch hunt instigated by conservative media groups. “Who in the world would call North Korea a paradise?” she told GlobalPost shortly after returning to her home in Diamond Bar, Calif.

Shin’s decision to leave the country was prompted by a high-profile incident at a lecture in December, when a high school student lunged towards her and threw a homemade explosive device. At the airport the next day, immigration officers declined her the opportunity to leave the country, ordering her to report to prosecutors.

In the end, Shin was not formally indicted and did not stand trial. She was instead deported on the grounds that her activities posed a security threat, a move criticized by the US State Department and others.

“The Ministry of Justice’s decision is completely flawed,” said Park Kyung-sin, a law professor at Korea University in Seoul.

He pointed out that the Ministry of Culture originally recommended her Korean-language book about travels in North Korea, called “A Middle-Aged Korean American Woman Goes to North Korea,” and even doled out the book to libraries.

Once there was a national uproar, the ministry abruptly removed Shin’s book from the list, along with a government-sponsored documentary about her travels formerly on a website.

“The only thing that has changed from the time of receiving the awards is that Chojoongdong” — a nickname for the three biggest conservative newspapers — “started labeling and decrying the talks ‘pro-North,’” said Park, the law professor.

Shin said she plans to sue South Korean media outlets for defamation, accusing journalists of misrepresenting her work. A few media reports suggested that she was acting at the behest of the North Korean government, and naively regurgitating regime propaganda that North Korea isn’t such a bad place after all.