As stated above: abuse is abuse, whether physical or psychological.
I'd guess that both in individual narcissism and collective narcissism the abuse often starts with a subtle form of psychological abuse. The abuser tests the audience, so to say. If there then isn't enough opposition or judgment from others than the target, the abuse will increase in evil.
A good example in my opinion is the Holocaust - a form of collective narcissism. It started with "small", subtle things. Indirect mockery in public papers turning into direct one. Okay, you got away with that! You can't have a radio or you can't go there. Okay, you got away with that too! You have to do this and you have to give all you have. Okay, you got away with even that! Then lastly you have to give your life too. (Making a long story very short).
As there is no collective opposition to the abuse, it will increase in evil every time people turn the blind eye to it. Sooner or later the abuse could lead to physical abuse and murder as was the case in the Holocaust.
In my opinion this increase in evil will apply to all evil actions. The mind of the perpetrator changes along the actions it takes. I think it is said in Talmud or somewhere that when you do sin and when you do it the second time, it's not a sin anymore.
The border of evil shifts place. What used to mean bad and forbidden, is no longer. The same applies to good actions. The more you practice, the further you want to travel.
Abuse breeds from abuse.