I'm not saying gay marriage is the catalyst. As I noted, the US marriage rate has been declining steadily for 40 years, much longer than gay marriage has an issue. But the push to redefine marriage (presently focused on gay marriage) is a symptom of the decline of marriage as a meaningful institution. If the traditional definition of marriage is to be abandoned, it will eventually become, "whatever you want." If two men or two women can marry, why can't two women + three men marry? Why any limits? If everything is marriage, then nothing is marriage. Marriage then adds no value to society. Once everyone sees that marriage adds no value, they’ll just stop getting married (except a few rubes clinging to their Bibles).