Yes. Marriage is premised on the understanding, nearly universal among societies that aren't terminally decadent

This is definitional reasoning- IE Any society that differs is by definition "terminally decadent"

that the best and most stable environment for raising children is a family that includes the child's natural parents

Actually this is increadibly untrue. Many native tribes in harsh climates consider the children of the tribe (who are the future of the whole tribe) to be someone to be raised by the whole tribe.

Scandinavian cultures had a long historical tradition of fostering out boys at ages 10-12 to other families.

European Middle Ages culture had children of elites raised by wet nurses and nannies

American Colonial culture usually had the children being raised effectively by single mothers as fathers went off to hunt, trap, whale or similar for months at a time.

You simply have no historical basis for your assertion.

Marriage fosters this environment by creating a permanent bond between couples and discouraging them from having sex (and thus reproducing) outside of that relationship

Again, not supported by history. Extramarital sex is more prevalent than not throughout history and cultures. Marriage in the sense that you are promoting it had more to do with property lineage in European Feudal cultures.

Marriage historically has had the function NOT of "rasing children" but rather of providing an inheritance lineage.

so no, producing children and giving them an environment to be raised in has NEVER been the "chief reason" for marriage.

History simply does not bear out your claims. You literally are making it up.