Why should North Korea be welcome to the 2018 Winter Olympics?

Many people would argue that North Korea should be welcomed at the 2018 Winter Olympics because the Olympics are about athletic competition, not politics. The original Olympic games in ancient Greece saw armies stop fighting in order to allow travelers to the games to pass safely through warring lands. This fact, along with the often perpetuated modern myth that the armies stopped fighting altogether, gave the Olympics an aura of being above warfare, hostilities, and hegemonic rivalries. The Olympics provided a peaceful way for countries (or Greek city-states) to compete without bloodshed.
This concept of the Olympics has continued through to modern times. The world gathered in Berlin for the 1936 Olympics, despite political strife between Nazi Germany and the rest of Europe. While some countries have boycotted games (such as the US refusing to go to Moscow, or the USSR declining to participate in the Los Angeles Olympics), the Olympics remain a place where athletic achievement and sportsmanship are favored over aggression and intimidation.
Lastly, welcoming North Korea to the Olympics could improve relations between strained countries. Competing against, or even just being with, athletes from around the world encourages camaraderie among countries. While welcoming the North Koreans at the Olympics will not solve all of the political tension in the region, it could serve as a real stepping stone to stabilizing the area.