I think they're the coldest, and most calculating. I do think they can be vengeful, but only if it makes sense, and it's really really worth the trouble.
We're really not, we just
appear as cold and calculating because we are quiet and often lost in our thoughts and philosophical mental meanderings. We live in our heads. People don't understand that about us and they just assume that we don't care about anyone or that we're cold. I'm sorry I'm just not listening because I can't! My head just won't shut up. I can't just stare into space and think about nothing. Perhaps INFJs find this concept baffling because they are very meditative people. My brain is constantly full of seemingly unconnected thoughts and concepts.
If anything, we think too much about things, including people. I sometimes feel as if I can read and sense peoples' emotions.
I have been told that I'm hard to read. Personally, I'd rather keep it that way. It's a defense mechanism and one that can come in handy in some situations. Who wants to be read like a book?
They're big softies though, on the inside. If they don't think you're an idiot and decide you're worth the effort to be in any friendship/relationship with.
Even if I do think you're an idiot, I'm still kind to people. I work in customer service though, so it's like an instinct now.
I think for a destructive intj, it's more that the end justifies the means - I think feelers probably have a greater ability to cause harm for the sake of causing harm.
A destructive INTj, I imagine, would be lost in their own code of ethics or morals that they would justify their actions. Think of the unabomber or some terrorist writing a manifesto. (We tend to have a lot of the "lone terrorists"). Some INTJs can become so disheartened and angry with the world around them that they may just start isolating themselves more and more until one day they explode. Think Travis Bickle, although I think he's more of an ISFJ.
The "ends justify the means" for INTJs doesn't really exist because we rationalize the law and tend to have our own moral code. It's not worth it to do A because it leads to B. It would be very hard to convince an INTJ that they "wouldn't get caught" because we have already gone through every single possible scenario 900 times over. Our ability to ruminate, overthink and over plan hundreds of scenarios would frighten us into refusing or chickening out eventually.
An unhealthy or "evil" INTJ would become so cynical that they either 1. choose to not care because they are a nihilist or 2. think it's better for the world to do B.
Think of Lenin and the Russian revolution. Why was the royal family assassinated? Because they didn't want them falling into the Nationalist's hands. It's very logical and devoid of vengeance, anger, or emotion. It was done because it was thought that it had to be done at the time for the greater good.
