In the Republic, book VIII, Socrates identifies as democracy's leading cause of corruption precisely that thing makes it seemingly so beautiful. In a democracy, citizens become inebriated with freedom (Euleteria). By making it the highest goal, people in a democracy end up leading democracy to its downfall.
Our boy Socrates was 2200 years too early, he might have learnt from ours boys Charles Fourier, Bakunin, Marx and others that democracy is never an accomplished regime, it needs to be defended at all time in a ceaseless battle against the worst parts of mankind, against our own turpitude and weakness, it's an everlasting revolution that dies as soon as it starts to be content with itself.