The idea that "nonduality" is "pure love and light only" is misunderstanding it. The idea that ANYTHING can be completely separated into "good vs bad" is duality. Nonduality contains duality but is not ONLY duality.

I don't know why you say that nonduality suggests negative things do not exist. That's not nonduality. Nonduality is about realising that a rose contains both beauty and thorns. The yin yang contains light AND dark. As does the human consciousness, and the world at large. Everything is one meaning that good and evil are all part of nonduality, not that evil doesn't exist.

The idea that there is unity underlying apparent separation, is not to say that evil doesn't exist!!! Even Buddhism has demons and angels in it.

You have an axe to grind against nonduality, but I'm sorry to say, you are misunderstanding it completely. It is not how you describe. Anyone who claims that nonduality is "love and light only, darkness doesn't exist" is lying to you.