you cannot remove the observer from the observed. Different interpretations are made of the evidence.
Well expressed. You are absolutely right, of course. It's not only in social sciences, but also quantum mechanics (as you know) that observers affect both the data and it's interpretation. (In SS, for example, the profile of an interviewer will affect the answers given by an interviewee) It's not only the you cannot separate the observer from the observed (although we have methods to try to overcome this), but the very questions we ask are loaded with value judgements.
On the other hand, there is a big difference between using scientific methods, however flawed, and cultural narratives (A system by which people organise their knowledge about the social world), which are non-systematic ways of making sense of life.
This is why we have therapists who are proponents of the MLC, like Jung and Jed Diamond, and then you have others who do not agree with the interpretation of the evidence as a MLC/depression.
The difference between Jung, Jed Diamond, and non MLC therapists is not just a question of the observer effect. Jung had a totally different historical context to Diamond, and his methods were at least partly intuitive, drawing influence from a wide variety of theologies and philosophies, but not neccessarily systematic clinical analysis. Jed Diamond has a completely different background, and shows (at least some) research supporting that the reason for irritable male syndrome is hormonal. (There is reserach to show that actually hormal decline is slow, constant from age 21, and only presents major decline in a small percentage of the population). Esentially Diamond's books are pop-psychology, have made him a fortune (an important observer effect is motivation and values), and are not at all in the same category as Jung.
There are certainly people who have psychological crises. My H almost certainly had one, and it wasn't his first either (he had one at age 21, and another at age 29, too). This was confirmed by a number of observers, some who had no idea of what he was going through, but noticed that he didn't seem himself, seemed lost, as well as by H himself (although he prefers to forget now). But that doesn't make it about midlife. Yes, he had traumas from his youth which shaped his personality (so did I, although I had a very safe and stable childhood compared to his; don't we all?).
My contention is whether MLC is really a useful category. Yes, it's useful for us, because we can pack up a range of behaviours and put them in a box, and it gives us some feeling of control, of knowing something about the unknowable, by labelling our spouse to be in a tunnel, and so on. I found it useful (emotionally) even while (increasingly) question its existence (rationally).
Yes, there are some traumas relating to aging, and Jung, Erikson and other psycho-social therories of personality development are useful for that. But many are not. My H's was not about hormones, or aging (despite my therapist wanting to put him in that box), it was more complex; it was about life (which had been unstable since was very young, with major emotional shocks), about stress (relating to external and internal pressures, his personality type and interaction with life events) and about chemicals too (statins have strong effects on behaviour, and almost certainly triggered his TGAs). Here on this site, there are some spouses who are extremely emotionally immature, some who are clearly psychotic, some with substance dependency problems, others who have different types of PD.
It seems to me that MLC is just too broad a category to be therapeutically useful. It would be better to break it down into sub-categories both for the person in crisis and for the people who suffer as a result of it. How can a therapist equally deal with an addict, a psychotic, a narcissist and someone in the throes of an identity crisis, or equally deal with their LBS?
All I know is that I need to work on myself and find my peace and joy again - and my wish for all of you is that you overcome this horrible hardship and that you find that elusive happy place once again, with or without your MLCer.
This is our reality, no matter what label we put on our errant spouse. A hard path, yet one which has been trodden by those who go before us, as well as those by our sides. Handling our expectations, our incertainties, and our heartbreak is made so much better in the company of the wise and experienced on this site.