So, South Korea, it's ok if you want to apologize, but, on average, most Americans probably don't expect it.
South Korean "blood" mythology is unusually strong, but it is not qualitatively different from other nations. Japan has a similar belief, though probably it is less strong now than it was 30 years ago. China was likewise appalled when Fox news reported the assailant was a Chinese student, and massively relieved when he was found to be 'South Korean raised in America'.
More broadly, consider this tribal identity in the context of these examples:
- Who, if anyone, should apologize for the annihilation of the Amerindian, or for American slavery? Why should they apologize? Who inherits guilt, and why? How do societies answers change over time?
- When can Germany stop apologizing for the Holocaust? How many generations are required? Does Germany have any moral responsibility to keep the memory of the Holocaust alive? (I'd say yes to the last, because of a much stronger version of #3, but it's debatable.)
- American soldiers, during the disastrous early days of the Korean war, killed South Korean civilians to speed their escape. (The US Military has recently confirmed this story after an internal investigation - very quietly.) Should anyone living today apologize? (I'd say yes, because there's clear institutional continuity in the US military, but it's a debatable point.)
- A euro-American wins a Nobel. Should black Americans be proud? Euro-Americans? The winner's mother? Euros? What if it's a Chinese American?
- Canada wins an Olympic medal in Hockey. Should Canadians be proud of their team? What if Montreal wins the Stanley Cup over the Mighty Ducks (ha!) and the teams are both Russian?
- Most citizens of the Arab world appear to hate Israel and Jews. A significant number were, at one time, sympathetic to attacks on the WTC. (I suspect that number has shrunk as everyone realizes that a crazed America is not a good thing.) Should an Arab-American apologize for this? (I'd say no, but I bet some apologize anyway ...)
- Should Idi Amin's parents have felt guilty for his crimes? What about his teachers?