Before kicking off with further arguments, a little commentary.
Stoic wrote:The key criticisms have been stated very often, oppression, lack of freedom, the killing of political opponents and civilian dissidents [...] But what kind of Argument is that? Not only is it circumstantial, but ignores the fact that Democracies and Republics do this as well.
Sure, all governmental systems tend to kill people, it's just that dictators do it
so much better:
As a baseline: WWI + WWII - about 70-80 million or so.
Now, dictators in no particular order:
Mao and his great leap forward: estimates differ but lets say 40 million.
Stalin: 20 million.
Jolly King Leopold in the Congo: 8 million.
Pol Pot: 2.5 million.
main sourceThere's more, but hey, who's counting. Dictators = responsible for the deaths of roughly 70 million people. ie. Four fucking guys, managed to kill nearly as many people as both world wars
put together. (And that's not even counting Hitler).
As I said: D is for damage control... And:

I'm gonna talk game theory a little.
If you want to get up to speed here's a link to an old blog post covering the basics.The main point in game theory is about iterated (repeated/sequential) games vs. one-offs. In a one-off, winner-takes-all-forever game, it pays no-one to play by the rules, or even to have rules in the first place. In an iterated game of X-duration, you might finish a game today, and play the same guy again tomorrow - who will remember how you treated him, and treat you the same.
Most dictators are usually playing a one-off against the people they dictate to. Their goal is usually simply to stay in power for as long as possible, and usually set things up, ala Kim jong il >> Kim Jong un, so that a son or relative carries on the family tradition of stamping heads. There is no opposing player to force them to play by any rules but transitory and self-derived ones. Like: "I won't kill anyone on days beginning with T unless they really, really bug me."
I'm not denying that a benificent dictator can't do great things for their country, only that in order to do so, they have to stay in power. ie. the 'doing good' part of the equation is secondary to the 'staying in power' bit. And to do this, you have those tried and trusted tools - monopolies on propaganda and organized violence.
But hang on, democracies do this too. Fair point. The difference however is Dictators use violence to silence dissent to a much much greater degree than democracies. And this is what kills people. You see, Mao didn't sit down one day and say to himself: "Fuck I'm bored. I'm gonna kill 40 million people." No. What he said was "I, by hook or by crook, am going to catch up to those damn Brits economy-wise, in fifteen years."
Trouble is, he was a fucking bumpkim from the sticks. A very smart, charismatic bumpkin, but a bumkpin all the same. And knew nothing at all about running just about the biggest economy on Earth, population wise. Classic example: Birds eat grain. Bad birds. So Mao declared war on them. The whole country was set to trapping, killing, poisoning and etc. every feathered friend they could find. It worked, the bird population was pretty much obliterated in a season. Yay. More grain right..? Nope. Because birds also eat insects. And insects eat everything. Result..? Mass famine. Lotta dead people. Another interesting tit-bit. You can boil down your dead granny and spread her on the fields as fertilizer. And your crap too. But if you do this, you also spread horrible diseases. Result..? Lots more dead people. But this is okay, because you've also destroyed most of your houses to make fertilizer anyway. The fuck-up list is endless.
And no-one ever said: "S'cuse me Mao-mate, but your economic policies are total bullshit." Because they'd have been shot.
Democracies, with their umpteen number of barriers to implementing new policies and their tolerence of dissent, don't do this as much. Damage control...
...And everyone else. Because Dictators are playing an exclusive "us vs. them" game, they are not really incentified (horrible word, sorry) to give anyone outside of the priviledged group informed political voice. Bad news for ethnic minorities, religious minorities, or any minorities at all. The only means of political expression left to the people is almost always mass protest, ending up as mass violence in most cases. Doesn't make for a stable country. Nor for an high average life-span. Democracies - even if you just want to cynically classify them as time-share sequential dictatorships - are forced to a much greater degree to curry favour from the various demographics and shape policy around their well-being to gather votes. Okay, you can pull in a lot of votes from the most common demograph, but then, so can the opposition. So then, to tip the scales your way, you have to find some way of appealing to the smaller demographs as well. Ad inifinitum, theoretically right down to demographs of one.
That's not what is important though. Many demographs are diametrically opposed to one another. ie. Political party X can either appeal to one or the other, but not both, leaving the opposing demograph to their opposition. But, if a third party can come along, and find some way of reconciling the two opposed demographs - in order to selfishly harvest votes from both and beat the opposition parties - then they will win outright. ie. In a democracy, there is always an incentive, however minor, on the part of the political factions for them to (a) get everyone taking part in elections, even if only to better exploit them and (b) to reconcile demographs with each other, again even if only to better exploit them. Which is good - well, less fatal anyway. eg. Politicians didn't give the vote to women because they thought "Hey, well, it's only fair." No, they gave the vote to women probably to shut them up. (jk.

) No, they gave them the vote so women would vote for
them.
The reverse of divide and conquer - empower, reconcile and smarm.