I found the descriptions of the history of marriage in Obergefell v. Hodges (2015) to be very interesting. Especially on page 6 where they are talking about the change that came from women getting more rights. It starts with “As the role and status of women changed, the institution further evolved. Under the centuries-old doctrine of coverture, a married man and woman were treated by the State as a single, male-dominated legal entity.” And then continues with “As women gained legal, political, and property rights, and as society began to understand that women have their own equal dignity, the law of coverture was abandoned.” These changes didn’t weaken the foundations of marriage at all. In fact, as new generations came to see this definition as normal it made the relationships that come from marriage much stronger.
If same sex couples were not allowed to become married, I think that the decline of marriage as an institution would be much worse and quicker due to the fact that even more people would not be getting married. The same sex couples that were trying to get married already had most of the benefits of a married couple, and so I think that if it stayed that way less people would get married since they could get the same benefits without the hassle.
As members of our church we already believe that our marriages mean more and are a bigger deal then the rest of the world. We have already defined our marriages as eternal through a separate ceremony that is exclusive to members that are worthy to enter the temple. I don’t believe that allowing same sex couples to be married by the states affects our meaning of marriage any more then allowing anyone else to get married by the state affects our definition of marriage.