You might notice that the opposite of Democracy Is Bad is Democracy Is Flawed rather than good. From this you might guess that Democracy on the whole is judged on a different scale than kingdoms, empires, and dictatorships. Saying that kingdoms and empires are bad or flawed won't raise any eyebrows. If it was flawed, it was because there was a bad king and we need to wait for The Good King. Indeed, monarchists often note that revolutions only happen against weak rulers (Charles I, Louis XVI, Nicholas II) rather than strong rulers, which means that the kingdom as a system is not invalid except for the weak rulers who potentially come to power. In the case of a democracy, a bad elected official is, by this light, a comment on the entire system, since it proves that A) a particular portion of the electorate chose wrongly or B) they were fooled by the candidate into thinking he was more competent or benevolent than he actually is. Either way, the people look bad in a way that subjects of a kingdom do not.
Democracy as such is always on trial for its effectiveness, and even today, it is judged on a perceived closeness or distance from a certain standard of perfection, from both the right and the left. From this you can derive the idea that democracy has aspects of it that are tied to a kind of utopian ideal for society. And in a certain way, it is.
Remember that democracy as we identify and live it today, not only in the kind of government (representative democracy) but also the democratic society, is a very recent development in the history of mankind. A modern democracy is expected to have universal suffrage for every adult, male and female, equal rights for individuals of all races and beliefs, protections for minorities, and a society of freedom of speech and expression. This idea of democracy would be regarded as "crazy talk" in the imagination of not only the ancients, but also the Founding Fathers, the Whigs and Tories of the 1700s, and to some extent, the Jacobins of the French Revolution. Universal suffrage only became a reality towards the end of the 19th century, female suffrage would achieve its centennial in the second decade of the 21st century in the Anglophone world, while France only gave women the vote in 1944! Switzerland was even later, in 1971.
In the ancient world, Athens and the Roman Republic believed that the vote should be restricted to elite property owners, that citizenship was a privilege rather than a right, and that it was okay for a class of people to serve as chattel slaves with no rights or voice in the government. Features that we identify as pillars of democratic society, such as civil codes, The Common Law, and religious tolerance came historically from Kings and Emperors such as Cyrus the Great, Henry the Second, and Napoleon Bonaparte. As much as the world has accepted Good Republic, Evil Empire as a given, the historical record has not always been as clear on that front as it should have been, since the representative elites of old republics were always wary of expanding the franchise, which allowed kings and emperors to ride to power on a surge of populism. This Self-Fulfilling Prophecy meant that the word "democracy" was often used to signify mob rule, and elites often believed that dictatorship swayed mobs easily. Their refusal to extend the franchise to these groups had no role in creating these problems at all. As noted by R. R. Palmer, it isn't until the latter half of The Enlightenment that you would find positive invocations of democracy, and the fact that the likes of Maximilien Robespierre made them only proves how radical and fringe these ideas were regarded back then.
The real reason democracies are flawed, as you might guess, is that every democratic regime must constantly renew and reform itself to survive. Kingdoms and empires maintain power by means of marriage and lines of succession, which, barring the occasional Succession Crisis, is easier to maintain on the whole than democracies. Democracies survive on the strength of their institutions and the power of their values and ideology, and the responsibility of each generation to maintain and build on these preexisting institutions and values while meeting new demands. A democratic person would likely distinguish the superficial ease of this sort of 'dictatorship' from the 'righteousness' of democracy.