It is probably a reference to nuance and the fact that the real world is complicated, with multiple competing interests and perspectives. Children learn history in lessons that often have an implicit good-guys/bad-guys story hidden beneath it, while educated adults tend to be able to handle stories that have fewer good guys and bad guys and mostly just a bunch of guys pursuing their own self-interest within a particular environment that provides a specific set of available options. The problem is that the latter sort of lessons involve more cognitive effort and do not lead you to easy answers that make you feel like you are a part of 'the good guys.' John Oliver, much like Rush Limbaugh, tells simple stories of the former variety; stripped of nuance and complications that are intended to lead the recipient to a specific and obvious solution or outcome.