There are different reasons why people get paid large salaries. Sometimes it's because they earned the money, sometimes it's because they stole it, and sometimes it's because they are skilled at abusing the political process to shut out their competitors. By default I assume people are in the first category, but sometimes the evidence indicates otherwise. Russian kleptocrats are in the second and third categories. UN insiders (whose salaries are fairly modest, by the way) are in the second. I suspect that executives at major commercial banks are mostly in the first category, but lots of people believe they are in the third, and not without reason.

As to your final point - I live in a country where it is uncontroversial to mention that the UN is opaque, massively corrupt, and whose permanent agencies are staffed by a connected group of permanent insiders. I didn't realise I was running up against some strange American taboo.