Reminds me that often German soldiers who were commanded to slaughter innocents had to drink a lot of vodka to be able to do it. Of course, the jihadi terrorists are totally committed to evil, unlike a lot of the German soldiers. But heavy intoxication will cover a person's conscience so they can do evil they would not otherwise be able to do.
A good book that had details of such slaughter and drinking is "Baba Yar" by - hmmm, can't remember the Russian name. Excellent book. Even though the author was a commie. He was a kid during the invasion and occupation of Kiev, and the entire book is his expierences and other first hand accounts. Riveting.
The author's name is Anatoly Kuznetsov if it is the same one I am thinking of.
Another book about the Einsatzgruppen worth reading is "Masters of Death" by Richard Rhodes.
....IMHO, it is not so much that the drugs,(yes alcohol is a drug)covers the person's conscience but that it allows suppressed evils to manifest.