Just as an aside: Germany, pre-WWI, was far from a democratic country, probably not quite as far away as was Russia, but certainly farther away than the UK or France. The pro-democracy activists were certainly not well-considered by the security forces, and were actively targeted by security services pre-WWI. Post-WWI, when the pro-democracy activists had control of the government, the security services actively supported the anti-democracy forces, such as the Freikorps. Had the Weimar government had reliable security services, the Freikorps would have been suppressed. No government will countenance armed rebellion, and no government will write into its basic law a right to armed revolt.
Trying to get back onto the topic of WWII Wehrmacht behavior.
There are two broad categories of war crimes: "ordinary" war crimes, such as using civilians as hostages, massive reprisals against civilians in an attempt to suppress partisan activity, and "extraordinary" war crimes, like genocide. Western Allies' armies were innocent of the second (one can argue that the Soviet Armies were guilty of the second during their suppression of reconquered territory, such as Ukraine); the WWII Heer was not, as the Wehrmacht was not loath to support the extermination of peoples in the invaded lands to the east of Germany. Did any German general or field marshal ever write a letter to his high command that mass murder of Jews or Rom should be stopped? High ranking military officers are supposed to exercise judgment, not be unthinking automata, so such letters would not be outside of normal expectations. One may not expect low-level officers or other ranks to exercise moral judgment concerning their orders, but they are still not automata. One would expect things like letters home to include upset at doing something (while "went into village and killed all the men, women, and children in reprisal for shooting Hauptmann Säuglingsvergewaltiger" would likely be censored, I'm sure that something would get through).
Of course, the major reason for the German invasions eastward was to replace the Slavic populations that were living there: the numbers would be reduced by starvation and the remaining population enslaved. At best, this would be "ethnic cleansing" (what marketing genius thought that up for mass murder and forced migration?); in the real world this would be genocide. It's just that nobody had thought of that word yet.