I've noticed that most of the pro-Empire posts here have to insert hypotheticals or brush off parts of Imperial doctrine/culture that undermine their argument. IF the Emperor was good, IF the Sith were fair and noble minded. IF this and If that. They aren't; no amount of what ifs will change that.
"Hypotheticals" are important to consider, because civilizations aren't static.
The reality is that the Empire is rabidly xenophobic and genocidal, elitist to an extent that even humans who can't use the Force are second class citizens and can be slain on a whim by their Sith overlords,
As someone else said, there are those trying to reform the Empire to change this. While there may be no outright massacres of aliens in the Republic, to say there's no xenophobia would be absurd.
and that any social mobility is an illusion unless you're a Sith.
If you're one of the millions (maybe billions) in Coruscant's undercity, or aren't part of the nobility on Alderaan, then your lack social mobility is all but guaranteed. In the Empire, if you prove your patriotism and ability to contribute, then you may advance (although there are obvious barriers to this as well).
Because even if you're a Moff, some punk Sith can still decide to part your hair with a lightning bolt and it's his right to do so. And even if you are Sith, you can be murdered by your fellows (who are encouraged to do so) if they want your stuff and it will be institutionally ignored.
Not exactly. The Empire has to put up a united front against the Republic on some level. You can't just go around slaughtering all the Moffs you want without consequences to morale etc., and while you are right about many of the Sith, they are capable of working together when necessary.
Playing Empire side, I've lost count of how many missions I've had to do that are all the result of Darth Ponderous or Lord Pretensor's grudge/pet project/cause being put forth and dozens/hundreds/thousands of lives and millions of credits wasted by the Empire. That seems pretty corrupt to me.
Not sure what you mean by this. The "pet projects" I've seen are of some benefit to the Imperial war effort. If they somehow hold it back for personal gain, they won't last long.
The OP also castigated the Republic for allowing slavery in other governments but the fact that the Empire openly enslaves hundreds of millions of people is all right somehow. There is no slavery in the Republic; it is illegal and those who practice it are criminals who are pursued and prosecuted when caught. If there is slavery in parts of the galaxy that are not part of the Republic, it is not their job to make other governments do what they want. They control their territory, their citizens, and their laws, not that of other people.
You mean "if" they're caught. Clearly groups like the Black Sun or the Exchange can and have operated under the Republic's nose. The Republic is also trying to win the Hutts' favour just as much as the Empire, and the Hutts are known slavers. There is also a moral argument to be made that "There is no such thing as an innocent bystander"---i.e. if the Republic doesn't even attempt to bargain with the Hutts to free slaves, but actually goes out of its way to ignore slavery when trying to win the Hutts' favour, they are complicit.
there's no such thing as a perfect government of any kind but any one that is based on the activity and will of the populace will be as flawed as people are.
Says you! Seriously, though, neither government is based on the will of the people. The difference is that the Empire doesn't pretend to be. Before you can have that kind of government, though, you need stability. The Republic is too bloated and corrupt, with too many different interests trying to pull its strings to be stable or effective.
The Republic as an institution is more fair, more open, and more capable of change and advancement.
It's not more fair or open to all of its citizens living in poverty. It's not more fair or open to those living under monarchies like on Alderaan or Naboo. The Empire is capable of change because it takes action. When the Republic takes action, it struggles to present a united front, as some worlds are simply abandoned to fend for themselves and ultimately are lost.
There will be corruption, because some people are corrupt but it's not the institutionalized and accepted corruption of the Sith Empire.
"Some people are corrupt" is just a meaningless platitude. Corrupt bureaucrats are corrupt because they have incentives to be corrupt in the system in which they operate. Corruption is not tolerated in the Empire. Certainly some beings become very powerful and murder/steal/etc., but anyone who holds back in the fight against the Republic or who cuts corners instead of ensuring efficiency is, well, removed. Incompetent or corrupt Moffs are removed, for example.
The corruption can also be expunged more easily; in a democracy, the government can be overthrown whenever the populace wants it to be and change effected. If the people want it and are willing to buckle down and do it, all the structures and systems are in place to effect change. It's not that it is perfect but that it can be that way if the people try hard enough. Reformers in the Republic build support, win small victories and build on them, gaining momentum until change is effected. Reformers in the Empire are killed.
First, the Republic is an oligarchy, not a democracy. Second, not all reformers in the Empire are killed. Those who openly declare their intent to act probably are, but even on Dromund Kaas itself a hidden Revanite camp exists.
In the Empire, there's no reason to want to change anything
This makes no sense.
and even if you did, there's no way to do it without a coup d'etat, the structure doesn't support that kind of thing. The more terrible parts of the Empire are, in fact, essential for it's functioning.
Same goes for the Republic. You can remove corrupt Senators who are caught being corrupt in order to keep up appearances, but the same bureaucratic games and monarchies and poverty and crime remain.
The Empire needs slavery; it couldn't afford to do all the things it does if it had to pay for all that work/food/equipment.
Sure it could. Besides, if the Empire needs slaves, it needs people in a good enough state to work. The Republic simply lets beings rot in the undercity of Coruscant or allows nobility on Alderaan to exploit others.
The Empire needs xenophobia because it keeps the ruling class from completely disintegrating into paranoid massacres that would fracture it immediately; it creates a boogeyman for them all to unite against.
Nope, and Malgus explains why this is wrong. For one, the Republic is a common enemy (not necessarily a "boogeyman"---regardless of who started the war, the Republic wants to destroy the Empire and hence is not a threat someone just made up), so you don't need to hate aliens. Regardless, xenophobia need not be permanent. Agents are constantly reaching out to other civilizations and groups on the Empire's behalf---a whole bureau called the "Diplomatic Service" is devoted to this.
The Empire's evil is part of the institution and thus any attempt to change it would have to fundamentally remake the institution itself.
If you can say that about the Empire, then you can say it about the Republic. But really, civilizations can and do change.