"what can be asserted without evidence can also be dismissed without evidence"

It's on the person who is implying a causation to state why they think that there is such a causal relationship.

Marriage success and child success have so many other things that they are correlated to: Home ownership, IQ, wealth, zip code, parental educational background, ability to talk about feelings, empath, conflict skill, ...,

So somebody comes around and picks "Marriage" out of this huge list, and somehow now the burden is supposed to be on the listeners to disprove it?

Maybe in high school debate class, it is. But for established societal norms that most people can see the benefits of, someone who comes in with a fringe belief is expected to provide a more interesting answer. If someone said “correlation is not causation” to the assertion that people who go to the gym regularly are more fit, people would dismiss them out of hand and treat them like an annoyance too.

That's an incredibly weak and overly dismissive counter to genuine examples of covariant potential causes.

It's seems clear that socio economic status has an enormous influence on child outcomes and is clearly intertwined with other factors.

Do better.

‘Everyone’? That is a vast assumption!