@XPD154 I think the ethics are pretty simple if we strip them down to the bare bones. If you were a 15 stone professional wrestler and your friend was a nine stone intellectual then would it be right to assault him and break his arm? The same rules apply with emotional power and insight too - badly hurting another who is much weaker than you in this regard is wrong, without just cause. It's harder to see the reality of this because physical differences are much easier to see and understand than differences in your strength of emotional insight.
But I wonder as I read your concerns whether you are aware that the risk you are worrying about is a twofold one. People of INFJ type are notorious for bringing others they care about too far into their own souls, which is how we can have such deep insights about them. The risk for us is that we let them into our core, and that can lead to all sorts of problems for us - of losing the ability to distinguish their emotions from our own for example, and even of softening the edges of our sense of identity. At its worst this can lead to an interdependence between the two of you, their problems become ours, and this leads to all kinds of problems for both of you. This happens of course most often when you use your gifts to rescue them in the wrong ways, but it can also happen when you are abusive to them too, because the interdependence is rooted in the emotional deeps and is non-rational.