i am kind of curious what sort of information is out there regarding the mental affect that participating in such mass murders had on the participants. Certainly, engaging in mass murder of tens of thousands of innocent people had to have had enormous psychological effects on the participants.
I've read quotes by Otto Ohlendorf regarding the fact that some men spontaneously engaged in brutal acts and approached their tasks with apparent zeal and enthusiasm. others were driven to drink and were forced to be replaced as a result of such activities.
What do we know about the effects of such killings on the participants and how the Nazi leadership confronted it?
I have only read one direct source on this topic and will structure my answer around that one source.
The Good Old Days: The Holocaust as Seen by Its Perpetrators and Bystanders by Ernest Klee
In this, what comes out is that there were three different responses broadly to committing mass murder,
The CO's did use the reasoning I mentioned above "a moral responsibility and political necessity" with their men to get them to continue to persist with the murder. The CO's sort of removed the human element from it and made it appear as though the Einsatzgruppen / camp soldiers were manufacturing assembly line workers doing their duty to the state.
From my other readings on Nazi ideology, it helps that the victims, Slavs, Roma people, Jews were all thoroughly dehumanised by then, thanks to incessant propaganda and this also must have helped remove the human element from it.
However, the firsthand reports in that book do suggest immense psychological reaction amongst the men doing the shooting, with many either sitting it out entirely (and not being punished for it), being sent to mental asylums, and commanders were also reporting increasing elements of moral stress, thereby necessitating the need for other...non personal methods of killing such as the gas vans.
If you are interested in this area, I strongly recommend this book, though be warned that it is absolutely sickening to read, it took me months to get through the 300 odd pages, as usually after a chapter or two, I would put it down and not pick it up for weeks on end.