Shin is a complex character because his existence within such a broken, dysfunctional environment as North Korean labor camps leads him to contain character flaws that are hard to stomach when he has enough distance from the camps to consider them. He claims PTSD, which is a fair claim because it is likely sincerely true, but on the other hand, he misses an opportunity to live with a clean conscience by admitting to his character flaws.
There are two major indications of those character flaws. First, his brainwashing makes him likely to compete against his family, a removal of filial piety and loyalty. He turns in his mother and brother for trying to escape, but then he also does the same thing. Second, during that escape, he vaults an electric fence by climbing over the dead body of the man who tried before him, and he doesn't stop to appreciate that person's death. This can be seen as a consequence of the camp's competitive nature.
That consideration could have shed even more like on the injustices of North Korea, but the shame of his guilt prohibits Shin from admitting his wrong. In reality, the types of sins that Shin has committed are insightful because they show the twisted ways that the North Korean government manipulates and distorts reality for its citizens. Without a reference point to healthy family life, given the tight constraints of competition (the government manufactures an ongoing scarcity to keep people frantic and weak), it is only natural that Shin would become self-centered and survivalistic.
