I'm going to have to question your logic here which seems rather circuitous to me. You're saying that because INFJs engage in doorslamming, because they feel it necessary, because they feel it is required for their well-being, that the case is closed. INFJs should engage in doorslamming with a clean conscience.
Horse hockey. The only thing this tells me is that INFJs feel doorslamming is sometimes necessary and that they feel it is sometimes required for their well-being. (BTW, not every INFJ on this thread gives the thumbs up to doorslamming. For example, I've received over 10 private messages from INFJs who wanted to tell me how much they disliked this common INFJ response to unpleasantness.)
The real question here is "Is it most expedient to let our emotions dictate our behavior?" Both ENFPs and INFJs are likely to let their emotions heavily influence their behavior, but is this wise?
Let me answer this question by quoting INFJ-extraordinaire Vicki Jo Varner:
So let me gently encourage you, Cafe, and the other INFJs who have expressed their dismay at me calling all INFJs out on doorslamming, to consider a new behavior today. Perhaps you can consider that while doorslamming may feel right to you, that this only feels like the right thing to do, because you are allowing your INFJ buttons to be pushed.
I think of the words carved into the Temple of Apollo at the Oracle at Delphi: γνθι σεαυτόν (gnothi seauton = "know thyself") and μηδν γαν (meden agan = "nothing in excess"). Truth and self-actualization lie in the middle path, without excess.
Nowhere are these truths more applicable than finding balance in our inherent tendency to choose one cognitive process over another, in this case choosing being decisive and purposeful over being flexible and spontaneous. Our preferred cognitive preferences box us into a way of seeing the world that we are often unaware. Balance comes using the most appropriate cognitive process based on the needs of the situation, not just with what we are more comfortable.
I do not doubt that doorslamming is most comfortable for many INFJs. But your implicit assumption is that just because something is more comfortable means that it's the best course of action is... well like I said already... horse hockey.
Let me remind all INFJs and any others who read this post that one-sidedness is not the answer! This is a lesson this ENFP has had to learn herself the hard way.
I don't think doorslamming is a good thing. It is a last resort. It usually happens because either the INFJ did not address imbalances, etc when they might have been manageable or they have been deluding themselves about the character of the person with whom they are dealing. Obviously it would be best to address problems earlier instead of letting things get completely out of balance and that it is a skill to develop. INFJs can have a tendency to allow people to cross their boundaries and to take too much without saying something and that is not healthy.
OTOH, a person that will keep violating another person's boundaries in a way that could trigger a doorslam is probably not the healthiest person in the world, either. I mean, if I leave my door unlocked, it is careless of me, etc but just because I left my door unlocked doesn't mean it's okay for you to come into my house and steal all my portable electronics. The fact that I didn't say, "Hey, my door is unlocked and if you ever need to use my phone or borrow some sugar, feel free to help yourself, but please don't take my computer or my iPod" does not mean it's okay to walk off with our iPod. Generally we don't doorslam sugar borrowers. We doorslam iPod pilferers.
Now obviously there can be unhealthy people of any type, but I don't think it's wrong to start locking your door when you realize your 'friend' is walking off with your electronics. I don't think it's crazy to feel like you don't want to be friends with that person anymore, either.
But I really think you are looking at the wrong end of the problem. Once a reasonably healthy INFJ has gotten to the point of doorslam, things have gone WAY. TOO. FAR. They've had enough. They are done. If you want to say they shouldn't have let it get to that point, I'll agree, but often the reason it does get to that point is because the INFJ is internally invalidating their concerns and their feelings about the relationship.
Further invalidating them by saying, "I know you are in the submarine and it is totally out of air and you are suffocating, but how dare you leave?? Why are you so selfish?? How can you do this to me??" -- All I can say to that is "WTF??? NO!"
If you truly want to help INFJs change this behavior, listening and validation are the ways to go, not further invalidation and preachiness.
You might ask how an INFJ can be made to feel safe enough in a friendship to address concerns they might have in a timely manner, for instance. Or maybe what some early warning signs that there could be problems. That would be constructive.
You could encourage INFJs to listen to their own feelings about how the relationship is going and to speak up when something bothers them. Maybe offer some suggestions on scripting for addressing particular issues. You could tell us that a good friendship is resilient and can take a little conflict.
This insistence on staying in the oxygen-depleted submarine, OTOH, is not constructive. The real comfort zone issue is the issue of not speaking up in a timely manner because believe me, no INFJ is comfortable with doorslamming. It sucks for us too, but it will be a cold day in hell before we let other people dictate when we are allowed to use our escape hatch -- and that is as it should be. It's self-defense -- and I may feel guilty and have nightmares if I kill someone who is trying to kill me, but that doesn't mean I believe I should have let them kill me.