Not enough to act like not seeing it means you don't comprehend how bad slavery is. For the record, yes, I have seen it. I have also read nearly a dozen slave narratives (including the basis for it). Listened to interviews by ex-slaves (yes, there are actual audio recordings by ex-slaves). I have taken college-level courses on the subject, and read various books on the subject.
No one is saying African slaves didn't have it terrible in the South, but that does not mean North Koreans have it any easier.
You should read up on North Korea. Dehumanization, back breaking labor, beatings, never experiencing a day of freedom, etc, are routine for millions. That and starvation.
The average North Korean is now physically stunted due to chronic malnutrition. And they are the lucky ones.