Darchei Noam

This is actually a continuation of a previous thread recently closed. In the original thread it was suggested that the (well adjusted) human mind was not capable of killing without negative psychological consequences. Basic hashkafic questions were raised but only answered with implied insults (that anyone who disagreed was “uneducated”).
Here is my hashkafic question again with a quote from the OU website on the subject of Darchei Noam
“based on a principle which runs throughout the Torah and which expresses itself in many different ways. This principle is formulated by Shlomo HaMelech in Mishlei,[2] where he says, “דרכיה דרכי נועם וכל נתיבותיה שלום – Its ways are ways of pleasantness, and all its pathways are peace.”
The Torah and Human Nature
One of the primary areas where we see the idea of “darchei noam” in the Torah is in the way the mitzvos relate to human nature. Although the Torah demands that we control and develop our nature, it does not place demands on us which will be irreconcilable with our nature. ”

Admittedly the subject at hand was not Mechias Amalek (the question I brought up in the original thread). Never the less, I would still like an answer based on this principle. Hashkafically how can following a mitzva be considered to cause definitive harm? And if modern psychology says that it does should we not just assume that such an opinion is no different then other areas were psychology is obviously wrong (I brought up gender issues)

Rav Gustman (lo alenu) had a child murdered in his arms by a Nazi. He then had an opportunity to be mekayim the mitzvah of mechias amalek with his own hands. Which do you think caused him PTSD and which do you think was a source of extreme satisfaction?