For some, the south is a dream turned sour and they are willing to return to their unhappy home.
Son Jung-hun first entertained thoughts of life outside North Korea after chaperoning guests at an international youth event in Pyongyang in the late 1980s.
As a trade official working under Jang Song-thaek, the recently executed uncle of North Korea's leader, Kim Jong-un, Son was part of the Pyongyang elite.
Those few days of interaction with foreign visitors gave him a vicarious peek at life beyond the confines of the world's most oppressive dictatorship and sparked his eventual defection.
But now, 12 years after he arrived in South Korea, Son has a new purpose in life: to return to the North to protest against the treatment of defectors south of the heavily armed border that has separated the two Koreas for nearly 70 years.
Son is one of a growing number of double defectors – political and economic refugees from the north for whom life in the democratic, capitalist south has fallen far short of expectations.
Catalyst for flight
The catalyst for Son's flight from North Korea was the abrupt end to Moscow's largesse bestowed on its communist allies after the fall of the Soviet Union. To earn hard currency, the Pyongyang regime turned to illicit arms exports, which Son helped to arrange.
But when he was accused of stealing $10 000 intended to facilitate the sale, potentially worth $30-million, of missile-making materials to Taiwan, he suspected he had been set up and felt he was a marked man.
"I knew what the consequences would be," said Son, who was detained for three months. "I was up against people at the top of the regime, so I took my friends' advice and got out."
In April 1997, he hired a lorry, telling colleagues that he was going to the countryside on business. Instead, he drove across the border with China, leaving behind his wife and their son. A year later his son joined him in Beijing and together they arrived in Seoul in 2002.
Son spent his first year of freedom performing menial jobs.
"I got to experience how people on the bottom rung of South Korean society really live," he said. "I soon discovered that life here was very different from what I had heard about in the north. "
Those early days laid the foundations for Son's work helping fellow defectors over the past 10 years – while plotting his return to a country he still claims to detest.
Son, though, is in a minority among defectors. Most savour the political and economic freedoms they dared not dream about in the north. Since the end of the Korean war, about 25 000 North Koreans – more than two-thirds of them women – have made the journey across the country's border with China, where they lie low and earn money to finance the last stage of their journey to the south, typically via Thailand or Laos.
But tighter security on the North Korea-China border and less sympathetic treatment by recent conservative governments in Seoul have stemmed the flow. According to South Korea's unification ministry, the number of defectors arriving in Seoul in 2012 fell to 1 509, more than 40% down on the 2 706 who arrived a year earlier.
New arrivals are interrogated to weed out spies then spend three months at Hanawon, a resettlement facility an hour south of Seoul where they are given counselling and coached in the practicalities of South Korean life.
After completing the programme, each defector receives government subsidies of 20-million won ($18 800) to find a home or a place at university, followed by monthly payments of 320 000 won ($300) for five years.
The allowance is barely enough to live on, Son says, as most defectors are indebted to brokers who helped them reach the south.
"It's not uncommon for female defectors to end up in the sex industry or men to get involved in drug dealing [to pay off their trafficking fees]," he said.
It is impossible to tell how many defectors have returned to the north. The unification ministry says it has records of only 13 double defectors, three of whom came back to the south.
Anecdotal evidence suggests the number is far higher. The South Korean JoongAng Ilbo newspaper quoted a former MP as saying that about 100 people had fled to the north via China in 2012 – a figure dismissed by the unification ministry – while about 800 defectors known to have arrived in the south are unaccounted for. Son says he knows of 70 to 80 North Koreans who are "desperate" to go home.
North Korea watchers say there are signs the country has launched a campaign under Kim Jong-un to woo defectors back home, reportedly with offers of cash, a job and a home.
Security agents have been visiting the families of defectors and telling them it is safe for their loved ones to return, a Reuters investigation found last year. There are unconfirmed reports of agents who have infiltrated the south offering defectors up to $45 000 and an appearance on TV.
Son reveals he is suffering from cirrhosis of the liver and has been given up to three years to live. Before he dies, he wants to be reunited with his ageing mother, who he is convinced is still alive. But he insists his motivation for returning to North Korea is political.
"I want the world to know how callously the South Korean government treats its Korean brothers and sisters.
"The North Korean regime might well use me for propaganda, or I might end up in prison. After all, I didn't flee because I was hungry. I left for political reasons.
"But I'm ready to sacrifice my freedom in the hope that North Koreans here can one day have theirs." – © Guardian News & Media 2014