This is another tricky topic. Well, Dictatorship relies on the skills and drive of a single person to administer government. If that person is both wise and benevolent then things tend to work out well to some extent(Singapore's founding leader Lee kwan yew is a good example). If the dictator is benevolent but not wise, their errors lead to harm. If wise but not benevolent, then people will suffer in the cause of expediency. If neither wise nor benevolent then people will suffer from cruelty and the state will be weakened under his reign. Removal of a dictator requires violent action and this typically leads to chaos harmful to the people and at least temporarily weakening the state.
Succession of the leadership often leads to the same violence if succession is in dispute and with each succession of the leadership it is a roll of the dice as to the quality of the new leader.
In a democracy, leadership perceived to be poor can be replaced lawfully without violence and routinely as necessary. Limits are typically placed on the lawful authority of government to reduce and prevent abuse of power. Its weakness, however, is first that the perception of the electorate can be distorted to support poor government or reject good government through campaigns of misinformation and second that when the majority rules it may seek to exercize tyranny over the minority.
Strong education systems can combat the first weakness and irrevocable legal protections can be implemented to combat the second, but a strong education system requires constant vigilance to maintain and new forms of tyranny are rarely easy to adapt to in time to prevent their use. Therein lies the problem as well.
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Ultimately, Democracy is superior in the transfer of power without the need for violence and while aptitude of either system of government for administration is subject to the skills and mood of the individual leaders, a democracy is less vulnerable to poor leadership since the authority of government is spread across several if not many people who can be replaced without the need for violence and the chaos that violence brings. Whereas there is no protection against tyranny in dictatorship that does not require a coup or threat of a coup, democracies can at least implement some lawful means to prevent tyranny, even if those means are imperfect.
However, that being said, as I said above, a well-run dictatorship/absolute monarchy/despotism, etc. can be more effective in achieving goals and taking initiative than even a relatively smooth-running democracy. Why? Easy. Dictators don't have to ask anyone for permission or apologize for not doing so. The more power is concentrated in the person with his or her finger on the proverbial button, the easier it is for that button to be pushed. The downside? While that button could be pressed for benign puposes like feeding the hungry and healing the sick, it could also be used for other bad purposes I.e the opposite
You might conclude that there is no more positive and effective government than that run by a truly benign dictator. If I could ensure that Jesus would be running my dictatorship permanently, I might sign up for that.
But that type of person, in my view, is seldom if ever the type to be drawn to that kind of power or to be willing to cut the corners necessary to achieve it.