In this passage from "The Perils of Indifference", Elie Wiesel uses the phrases "black gates and barbed wire" to evoke emotions on the reader.
It seeks to convey the dark and gloomy atmosphere of the camps where Wiesel and the rest of the Jews were imprisioned and tortured while world leaders concentrated on fighting each other. He wants to provoke a sense of guilt and remorse for not helping the Jews out earlier.
A reason why would be that if parent's pressure their kids into doing sports, they won't really want to anymore, and as soon as they can they will quit.