It is very hard to dispute this idea. After all, all governments are based on human beings and all human beings are flawed.
We can see that every kind of government is susceptible to degenerating and becoming corrupted. A government that has one ruler can degenerate easily if the ruler is cruel or greedy or simply incompetent. But even a government like our own, with checks and balances and elections can degenerate. It can get to the point where we are today in which the parties and the politicians care more about getting themselves elected and making their opponents look bad than about truly trying to solve the problems we face.
Madison said that if men were angels government would be unnecessary. But people are not angels and therefore any system of government we have can become flawed and stop working correctly.