Whether we choose to recognise marriage in law and culture or not, when people decide to build their lives together, it changes how society views them; the presumed near-absolute solidarity between two people contributes to a kind of shared identity; some phrase this as becoming family, but I avoid that phrasing because I think that bond is usually stronger than can be presumed of family; there may be things I would do for family that I would be less likely to do for others (although I do admire Mozi's writings on the topic so the strength of this is heavily nuanced), but presuming a common identity, common perspectives, and any duty to agree? Absolutely not, while if I ever do get married I would expect some degree of all of these.
Politics and corruption track this kind of relationship; the wife of Justice Thomas's involvement in Tea Party is seen as inappropriate because of her husband's position; supreme court justices are supposed to be politically neutral (and there are many traditions that are meant to provide the appearance/reality of that). This recently came up in French politics, where François Hollande's consort (an outspoken journalist) has been unexpectedly high-profile, and has taken steps to antagonise his ex-wife, fellow politician Segolene Royal. There are restrictions in some countries barring relatives or spouses (broadening the topic slightly here) of political leaders from either seeking their own political office or working in positions that might be regulated/impacted by the decisions of their kin/spouse.
There's some natural tension here; while in centuries past and in older legal systems, families were considered as much as or more of a unit of society than individuals, in modern times in the west we've abandoned the hierarchies of responsibility/property for more of an individualist set of laws. This process is not complete; many western countries have inheritance defaults (and sometimes mandates) for people in the same family unit, people may be immune from being compelled to testify against spouses/kin in some areas, and there are at least societal expectations that come into play.
Individualism, like nationalism, may be only a few hundred years old in its current form, but without historical sophistication it takes considerable effort to question it or imagine an alternative; it's so much a part of our cultural fabric that its exceptions feel more structural than it does. Being able to investigate it remains useful in discussions on the meaning of marriage though; we likewise need to be able to clearly think about and address the possible dangers of presumed strong fealty between family members when that fealty might extend into business, public office, and the like.
There are some areas where we should probably expect changes in family life, often relating to the traditional role of women; notions of family that limit the ability of people to self-actualise (preventing women from having full careers) are not acceptable in modern times. This is most easily seen in national leaders, where the wife or consort frequently cannot continue their career effectively while their husband is in office; Michelle Obama's law career was effectively put on hold by her husband's presidency, while Jill Biden provoked some controversy by continuing to teach classes during her husband's vice presidency.