[Theory] I've always failed to see how "Narcissism" is negative

[ΛΟΓΟΣ]

So, your definition of Narcissist is "someone who thinks they are extremely special, when usually they aren't, and when you inform them of this they become enraged."

That sounds more like a sensitive or unfortunate state; but the way they are spoken about, narcissists are painted as Harmful to others.

"How I'm recovering from dating a narcissist" etc.

i dont see how that's mutually exclusive. elliot rodger was a narcy, he killed 6 people, and people just find him pathetic (he was)