Hopkins, Lisa. The Shakespearean Marriage:
Merry Wives and Heavy Husbands. London: Macmillan, 1998.

Thesis: This is a book with an agenda. Hopkins is a feminist and she writes to enlist Shakespeare in her cause, which is to challenge the view of marriage as a natural and loving union of a man and a woman. This is how she puts it:

I shall argue, then, that Shakespeare habitually dramatises marriage as both redemptive and painful, a state which may well be socially indispensable but is not, however hard Puritan (and indeed contemporary) rhetoric may protest to the contrary, 'natural'. In many ways, I would wish to align Shakespeare here more closely with an aristocratic ethos, which minimised the role of love within marriage, and stressed instead compatibility of background.   (9).
In the short section on Macbeth (four-plus pages) Hopkins devotes most attention to metaphors and motifs of marriage, fertility, and sterility. There is just one paragraph on the relationship between Macbeth and Lady Macbeth. In that paragraph Hopkins asserts that "Lady Macbeth's view of marriage, while in some ways companionate, is also relentlessly premised on sharply drawn sexual distinctions" (148) Then Hopkins draws to a close with her moral:
What the Macbeths' relationship shows us, then, is perhaps that when the genders are kept so firmly apart, and when what lies at the heart of marriage is a sexual relationship so clearly predicated on sexual difference, it can work to break down the companionship and union altogether.   (149)

Bottom Line: A boulder of a conclusion teetering atop a pebble of evidence.