Causation Versus Selection

This article in Psychiatry Weekly discusses the research on whether the social selection or the social causation theory best explains why married people have better MH outcomes. Generally quite reasonable, but what caught my eye was the information that sociologists come down strongly on the causation side - that social relationships like marriage provide a protective factor - contrasted to the selection theory which holds that it's the healthier people who get to get married in the first place.

If I'm reading this right, I have to ask - is there any sane person who questions the idea that selection is at least a significant factor?  Most people offered the two theories would say "I think both are probably somewhat true."  Nailing that down with real data might be tricky, but I can't imagine anyone would argue that there is little or no selection. Anyone know enough sociologists to know how firmly they come down in the causation camp?

Additional note:  the offhand remark that same-sex marriages might be more protective because they fought so long and hard for recognition is exactly the sort of blather that shouldn't be in a research article.  It might be absolutely true.  But we aren't shown any evidence for this, just a conventional wisdom assurance that functions as birdsong, letting us know where the researcher stands on the issue.  It would be bad enough in an op-ed.  In a professional context, it's just ridiculous.