the south wasnt any better.

People escaped from the north toward south.Same as in Germany they moved East to West not the other way around.Pattern repeated all around the world of people escaping socialism into horrible capitalist exploitation.

The US had internment camps during the 2nd world war.

and that is preety much agreed to be one of the worst things US did through the war while plenty of socialists excuse literal genocides as "kulaks/rich deserved it".

Vietnam and Cuba, for example, didn't do this.

Both these nations murdered political opponents to the revolution and expelled or caused huge swaths of people to flee them risking their lives.Political prisoners were common for both Castro and Ho Chi Minh murderous authoritarian regimes that were targeting evil landowners that had no place in socialist utopias other than 6ft underground.I guess they were not people as clearly "You said socialist countries developed gulags or equivalent shortly after taking power. " the system of mass opression and mass murder was in place and murdered thousands upon thousands.

That said I dont personally believe marxist leninism or even straight up marxist communism is doable today (again, not a communist).

What is the magic pill that will finally make socialism work?

No wonder that Portugal is being surpassed by more and more East European states because at least we seem to learned our lesson that were forced to by the USSR on what socialism is and it's flawed ideology but at least you guys voluntarily want to built that failed utopia so have fun.

I am certain that more western academics have worked out problems that comrades in the east were too limited to solve just few more millions of kulaks have to be murdered and utopia will finally arrive.