Dual relationships are quite nice, but the problem is they cover up your weaknesses so much, that you stop improving yourself. This is very dangerous.
If you spend too much time with a dual partner, the more dominant person in the dual relationship will totally pound the other one in submission (and not in the good way) where the more passive partner will totally stop taking care of themselves and just wisp away into nothingness because the dominant person is totally taking care of the physicality of the situation. This can continue so much so that they develop health problems. Caregivers dominate their infantiles; aggressors dominate their victims.
I notice this with SLEs. They ALWAYS protect me if we're playing sports together, and so I can't learn myself. They just have a powerful physical presence, and will just completely take over the role while we're together so I don't have to worry about that at all. This is very relieving and it energies my mind so I can focus on talking to people about their issues and inner worlds, which is what I wanted to do anyway. But if I don't use SOME myself I will get very weak and sick. So I have to spend some time alone, or with other IEIs where I can practice my on my own.
Dual relationships seem the best option to encounter environmental stress, so they contain the least amount of neuroticism. From a purely Darwinian standpoint of natural selection, this makes them the most ideal. But if you spend too much time with each other, this seems to backfire.
With our highly technological world, we don't have to worry about environmental stress as much as we did back when socionics was developed, that's for sure. So people are weaker and out of shape. Now more than over, most people (in America at least) just don't need their duals, as our brains allow us to transcend the natural order of things by understanding it and looking down on it. (I'm not trying to put 'natural' as any kind of ideal, the Darwinian life of doing nothing but responding to environment stresses so you can mate is painfully unpleasant for humans and we seem to do everything we can to avoid it, unless we're trying to show how manly we are. But we're able to overcome it with our brains, and I think we were of course meant to. We conquer the world by becoming softer and smarter, not stronger and dumber.)
To get strong and fit yourself, you need to hang around with somebody that just can't/won't cover up your weaknesses. Identity seems good for this. As they'll point out/educate you about your weaknesses but will be unable to do it for you.
So it all works in the balance and a healthy life would need both. If I'm with a dominant person, I can still enjoy talking with them very much but it ALWAYS has to lead to an activity, as they have the natural urge to conquer things in their physical environment. But this just isn't really needed as much in this day and age as all the upgrade to our tools keeps on becoming well, 'faggier' and 'faggier.'
So therefore, maybe that's also part of the reason why we tend to ignore our duals in situations, eh?