By not understanding that the Imperium was always meant to be seen as "good", shows how little you do know 40k. The tragedy of the entire affair is that by modern metrics, the Imperium is awful, horrid, and rightly condemned. But by examining the greater context of the 40k universe, the Imperium is shown to be doing well, and is acting as best a "good guy" as it can. The horror is that the Imperium does awful things and is less evil than the vast majority of the factions. When an extremely dark shade of gray is the lightest you have, things start to look different.
Especially coupled with the Imperium of the 30k and the ideals it espoused, and the reforms that Roboute is sure to make, the 41st Millennia Imperium is atrocious, but is one of the biggest "goods" in the galaxy. This is the horror and the tragedy of the 41st Millennia.
There's been a very marked shift in the tone of 40k from showing the Imperium as simply a less terrible option to showing it as uncritically on the side of light as the setting exploded in popularity. The 40k of yesteryear showed the Imperium as a dysfunctional hellhole with the worst of fascism and feudalism combined in an endless morass of inefficiency and pointless brutality for the sake of brutality. However as the setting started getting more and more popular the setting grew less and less critical of the Imperium. What started out as a parody of fascist rhetoric by showing the kind of hellhole the universe would have to be for fascists to be right about literally anything gradually became more of a standard Space Opera protagonist civilization but with more religion and more skulls and more xenophobia. Space Marines went from bloodthirsty psychopaths to heroic soldier-knights, the Imperial Guard has pretty much shifted away from comically obsolete world war one/early second world war tactics meant to be as wasteful of human life as possible to essentially being a modern army and since Ibram Gaunt and Ciaphas Cain became popular more and more commissars started becoming more benevolent like them when they were supposed to be an exception.
Meanwhile the Tau were basically the opposite. When they were first introduced they were far more heroic and positively portrayed than they are now since they were meant to be more of a standard science fiction civilization in 40k's brutal gothic space fantasy. They were meant to stand out amidst the brutality with shining optimism and cooperation and a very unusual (for the setting) aesthetic and emphasis on precision ranged combat with generally practical(ish) weapon systems. However there were people who almost immediately started complaining that the Tau were out of place (missing the whole point), that they were "too good", and generally whining loud and long enough to get GW to start putting in more and more darkness to the Tau. Now the Tau ethereals are mustache twirling villains and the Tau Empire is probably more negatively portrayed than the Imperium is on average.
It's much like what happened to the Galactic Empire in the EU before thankfully all the fascist apologist trash from the EU was forever jetissoned from Star Wars canon. Empire fanboys started to do the writing for the EU and started to do a lot more of the buying. So the Empire went from the original vision of a pointlessly brutal jackbooted regime with no redeeming qualities that blew up planets full of innocent people for the sole purpose of terrorizing people into submission to a force for order while the New Republic became a blisteringly incompetent bunch of morons incapable of making decisions or stopping the Galaxy from falling into constant crisis; in effect making the Empire
right. Which was pretty thoroughly disturbing.
While the Imperium is considerably more justified than the Empire; I find the tonal shift in the Imperium's portrayal kind of offputting, and it's why I like Horus Heresy authors who try to portray the Emperor as quite simply wrong and that his way was in fact, not the best way or even necessarily a good or even workable way. Like the existence of the Interex in the Horus Heresy setting or the Diasporex largely served to show that the Imperium could very well be
wrong about literally everything. You had much more liberal societies living in peace with xenos who were integrated into their societies and who were quite capable of fighting against Chaos without any need for the Imperium's brutality. The Interex could mass produce supersoldiers who could fight on even if not superior terms with space marines without needing to rip small boys away from their homes and could preserve and advance technology without any need for the Mechanicus' dogma.
To the point where Chaos found them enough of a threat to make sure that Horus would destroy the Interex and make their way of doing things forgotten. Chaos found the Interex's way of life far more threatening than the Imperium. Chaos is quite happy to have the Imperium exist, feeding it endless misery and negative emotions. If the Interex achieved a similar degree of success the Chaos Gods would
starve. Hence working to actively annihilate the Interex while merely setting up a ten thousand year stalemate with the Imperium.