Genuine knowledge (i.e. accurate, objective, comprehensive and unbiased information) about Nazi Germany (or any other object of historical research for that matter) can be obtained only from sources that are genuine history – not (usually political) propaganda.
Consequently, to obtain this knowledge, one needs to be able to tell genuine history from propaganda. To do that, one obviously must know the key differences between the two.
The most fundamental difference is, obviously, in key objectives. The only fundamental objective of genuine history is to discover, disseminate (preach, if you will) and defend (if necessary) historic truth.
The fundamental objective of propaganda is usually political – to seize and maintain political power (which typically includes manipulation and control of the social group in question).
Genuine history is all about truth; consequently, it is always objective and unbiased. Propaganda is all about manipulation; consequently, it is always biased (often very heavily biased).
Genuine history always seeks to create an objective and accurate (and thus comprehensive) picture of the object of historical research. Consequently, a genuine historian always strives to collect and properly structure all relevant indisputable facts about the object in question and analyze them using only rock-solid logic and good old common sense.
And accepting whatever conclusions these facts, logic and common sense would lead to. In other words, genuine historic research contains only truth and nothing but the truth.
Propaganda seeks to achieve certain political objectives. Therefore, it strives to create the picture of the object in question (i.e. Nazi Germany, Soviet Union, etc.) that will be the most valuable for the political objective in question.
Consequently, a propagandist (consciously or unconsciously) selects only information that supports the “politically correct” objective and structures it in a “politically correct” way.
Using only “politically correct” logic, of course. Thus ignoring all indisputable facts that paint a “politically incorrect” picture and often ignoring good old common sense. Thus inevitably creating grossly distorted and highly incorrect perception of historic reality.
Genuine historian does not make moral judgement (only functional and legal). He or she only investigates what happened and why, who did what and why, what were the intended and actual consequences of their decisions and actions and why they were different (if they indeed were).
Propaganda is all about making moral judgements as the latter are one of the most efficient tools for manipulating individuals. And while a genuine historian can (and often does) make honest mistakes, propaganda (i.e. so-called “Holocaust denial”) is full of deliberate lies.
Genuine history is strictly logical; there can be no positive or negative emotions in research deliverables created by genuine historians. Propaganda is full of powerful emotions because they are very efficient tools for manipulating individuals.
A genuine historian serves only the Truth; propaganda serves political parties (e.g. Communists), social groups (e.g., “liberals”, “progressives”, neo-Nazis, etc.), “special interest groups”, etc.
A genuine historian MUST publish the Truth that he (or she) has discovered even if it leads to very “politically incorrect” conclusions and highly undesirable consequences (for some or even the overwhelming majority of the population). Even to the reincarnation of the Third Reich.