The unfortunate part of this all is that our functions are the same ones as the ISFJ functions. So basically our Mr. Hyde is an ISFJ. And from the posts above, that can be a really manipulative type, unfortunately.
We are always talking about "working on our feeling function" but what happens then is that we can turn into ISFJs or even ESFJs. While I am sure those personalities have some strengths, they can also be quite dangerous.
I've just realized that I, unfortunately, turned into an ISFJ on some of my friends. I guess I just want to warn all the other INTPs that if you do try to increase your S and F, be aware that you could become very much like an ISFJ.