My arguments are human history, most oppressive monarchies have been destroyed by humans via revolution (some have been taken over peacefully), when the rich have too much power the poor kill them, because there are always more poor people than rich people, that has happened many times in many countries throughout human history.
When the rich take over a government it is no longer a democracy it becomes an oligarchy. The rich do not rule by democracy they destroy democracy and create an oligarchy (they may create an illusion of democracy but when laws/rules are created/destroyed that only benefit the wealthy minority that is not a democracy). The problem with political education is a symptom of oligarchies/monarchies, when the wealthy are in charge they do no adequately fund schools for the majority because an uneducated population is easier to control.
I do not agree that hereditary monarchy is more reasonable, it is just another form of government where the minority wealthy control everyone else.
Democracy does not fail it is destroyed when the wealthy take over a government. Democracy only works when everyone has equal voting power and the decisions made with that voting power benefit the majority of the population. When money is introduced into politics and government officials are bribed and bought the government is no longer a democracy because voting power is no longer equal. If those government decisions continue to increase wealth inequality and the government starts becoming oppressive than we will just have history repeating itself and another revolution...