....Would they? Remember a big part of the Great Crusade is the Imperial Truth, they might get a run down of really, REALLY basic things but huge portions would either be omitted or lost in translation. Furthermore, much to the Imperium doesn't think of the Emperor as the Emperor, they think of him as the Sun God, or the Fertilization God, or whatever is easier for the Imperium to manage. They turn their eyes the other way for the appropriate sum of money or just because it makes things easier to control, the things you and me take for granted as common knowledge in the Imperium is known by next to no one.

In all likelihood, many worlds don't know what a Space Marine even is.

Oh I'm not trying to say that they'd get remotely accurate information, like at all. But, for these segments of the Imperium to look at the Emperor as a Sun God or whatever, well therein lies what I mean. They have to mention the Emperor's Ascension, that's just how any religion works, they need a creation myth. Thusly, I think the Heresy would get some very edited interjection into the Emperor's Ascension myth. Plus, I recall in many stories people being aware of old legends of Space Marines turning on the Emperor, as an ingrained hatred of them. Though I'd still say a majority are completely ignorant, among civilized worlds, fortress worlds, shrine worlds, and such there would be a lot of people taught the Official Version of Events(mostly lies and exaggerations)

Or he's just always been, and always will be. The God was always there and he made everyone else in his image.

The flipside of the coin is there are plenty of Imperial Officers who have a Space Marine dropped on him and he has -no- idea of what he is, to them he might just be a really big human. It's also further compounded by the fact that it takes forever for the offical version to reach anywhere, if it's even accepted. There aren't even any computers because AI has been outlawed, the best you have is a human brain jacked into an electric box to transmit signals locally.

The Imperium contains, roughly, 500 trillion people. Traveling from planet to planet can take anywhere between 1 week and twenty years in the warp, and when you get there the locals can either reject your statements and file them away or twist what you've said violently, the Imperium is a propaganda machine but it's neither an efficient nor coherent one.

I wouldn't surmise that even the Imperial Creed would go for, "this is just how it has always been," particularly with the Great Crusades being the Golden Age they hold up as the ideal they once were. Thus would go for the Space Marines, it think it would be less they hadn't heard of them, and more they are just legends to the people (unheard legends in some cases) and since they've never actually seen one, when they do it's way different than they'd imagined.

But given the inconsistencies, size of the universe/ip, and lack of clarity in these sorts of details, this isn't really a debate that has a right answer. So I'll conclude, in my view it makes since that the legends of the Imperial Creed would include some heavily falsified information of the Crusade ending in tragedy, and the Emperor truly rising to godhood from that tragedy.

Fair enough.

Well I think the the only "good" Chaos Space Marine would be Talos. All the views of chaos are going to be negative because (most) people don't think killing people for fun or torching whole worlds is ok. We could definitely talk about what legion is "moral" compared to each other. So for example:

World Eaters: Probably the most "Evil" of the Traitors. They kill everything or mostly everything, including themselves... The best part is their encouraged to. Blood for the Blood gods! Makes no difference what blood, just as long as it flows. If they kill, great! If they die, so what?

Word Bearers: Very mixed "Moral values". They still stay somewhat organized with their original legion and they will probably wont screw each other over as much as the above legion. Don't know how they treat their slaves or each other individually. Probably one of the more "Morally Grey"

Night Lords: Even though the mighty Chaos God ADB has painted a "nicer" image with his Night Lord trilogy, they are still evil as shit. They like to maim their prey and let it run off so they can go hunting. If they are in space for too long they play Hide and Seek (with lightning claws) with their slaves. They also care very little about there fellow legionnaires or legion as a whole. "Oi Talos! That's a nice sword you got there...". I rate them second in "Morally Evil".

Iron Warriors: While there tactics are very calculated and cold, there is a strong connection between the individuals. Instead of killing their squad member for his Neato red glowing sword, they hold back their temptation because it does not help their (grand) company. From what I have also read there is some kind of honor and identity with being a son of Perturabo. Now if and Iron Warrior company ran into each other they might look the other direction or help each other, but you might get sacked if your any other Legion. Probably with the Word Bearers in being more "Morally Grey".

Black Legion: Depends on who is the individual in charge but usually a little more organized then the other legions. Don't know much about the black legion, but I think they are one of the largest legions and so it really hard to group them all together.

Everyone else: Either they are robots now, not even 100% real, random warband, or IDK anything about them.

While I agree the level of comradery that Talos had with his slaves would be more of an ABD anomaly, I'd say the lore from that does give an overall atmosphere significantly less bleak that other Chaos Legions/Warbands. Yes, even on that ship, Night Lords would sometimes hunt crew for fun, but they also had an undersociety of slaves. I think ranging from band to band, we'd find a spread of treatment for their slaves. I think most would be ignored aside from those that perform crucial duties, and these are fairly safe, while the rest are left to their menial jobs or to scrape by, of course never knowing when a some legionnaire might kill them for kicks.

And of course there are the Full Terror segments that have lost themselves to the pursue of fear. I imagine that any systems that don't run on daemon drives have expendable crewmen that are cycled through rather quickly. So those ships would be pure hell.

Blood Gorgons

I'd argue that they're all good or neutral. Except for the World Eaters who don't really give a rat's ass and are just along for the slaughter because the Butcher's Nails are singing in their brains, any legion still acting as a legion has a purpose. A goal. Even individual warbands are still all working towards a common goal at the end of the day. "Bringing down the rotting edifice that is the Imperium." The revolution that the Heresy started isn't over yet, it's just in remission.
Can you imagine how that must smart, Lorgar and his entire legion was brought to kneel in front of his father, forcefully, because he was caught worshipping the emperor as a god. Now the entirety of his Empire has followed suit and think themselves righteous for it. I'd want to tear it all down too.
The Octed are funny sometimes.

Thats not very accurate at all.

Chaos is evil because of the 'part' of humanity that is negative, but humanity does not equal 100% negative emotion. Yes it is a greater percent of negative compared to positive emotions but the Emperor has shown it can be lessened ... but now that he's a corpse throne and his ideal has been twisted into something else it is failing again. Legions of Chaos are humanities darkside given form but there is also plenty of good guys out there still.