Yes. You're right. I "studied" personality disorders, specifically narcissism and their symptoms/behaviors for a little while. My uneducated thesis is, there can be more to these behaviors than can be explained simply by dopamine. At least in the case of personality disorders, they often have very high intelligence. I think its more than just dopamine. 

To be clear, what I'm about to say is not excusing the behaviors, I want to help people defend from people with PDs, or even help the PDs.

It's also something I learned/experienced is, that I often don't believe people with PD's are fully aware of their behaviours and how they affect other people. Or they might but are very ashamed of it but dig deeper. Its a drug addict behavior. (there is a name for it but I cant remember)

Specifically for people that are not engaged in a power asymmetric relationship, it CAN be quite easy to learn about PD's behaviors and block/disarm them. Again most PD's are quite intelegent, they realize this, and are presented with 2 options: Stop because it doesn't work on you, or double down until you walk away. The more experienced generally take the former, younger or lower intelligence will often take the latter. 

My heart goes out to those in asymmetric power relationships with PDs and the like. Where when the PD is presented with the same choice, their decision to double down can cause some serious abuse to the lower power individual. 

You are now telling the affected person you have discovered their vulnerability and are using it to defend yourself. That's why it can be dangerous. This is why so much of psychotherapy treatments fail due to the patients insecurity and their toolkit (or lack thereof) used to overcome them.