Agreed. A character's naivete - even to the point of stupidity - is not necessarily a plot failure, especially if it illuminates how people often listen to the worse angels of their nature. It's not unrealistic either: there are schools of thought that hold that Western Trade Policy on Chinese economic inclusion in the 1990s and Wilson's 14 Points in 1919 were both mainly powered by wishful thinking. Hoping for the best from people is usually a bad plan, but it's one that gets used from time to time, even when the stakes are high.