I have always been puzzled by the assertion that Gay Marriage breaks up the family unit... It isn't like many currently married couples are suddenly going to collapse so a partner can enter a gay union

DIVORCE broke up the family unit and more specifically the change in the social acceptance for Women to Divorce

Back in the day a Woman was expected to stick with the marriage through thick and thin and would be socially ostracized if she tired to get out - now that just isn't the case anymore in most the Western World and that is why we see an increased number of "Broken" families - because it isn't a social faux pa to cut and run if it isn't working out

As to why its effecting a certain class more than the others - the "Working" class in particular have always been vulnerable to Drink, Drugs, Violence and (probably most importantly since it generally leads to the others) Poverty - all of which are significant causes of divorces