Positive benefits of marriage 

• Higher incomes and greater accumulation of wealth (and avoiding the loss of income that tends to follow the breakdown of relationships) See, for example, Zagorsky, Marriage and Divorce’s Impact on Wealth

  http://jos.sagepub.com/content/41/4/406.short

• Improved health and wellbeing. One study suggests that ‘the size of the health gain from marriage is remarkable -it may be as large as the benefit from giving up smoking’

  www2.warwick.ac.uk/fac/soc/economics/staff/academic/oswald/healthlong2005.pdf

• Cohabiting people are significantly less happy in their relationships than married people, and children are happier when growing up with both biological parents (Understanding Society survey, ONS)

• A typical finding of cross-national studies is that “much can be done to improve child wellbeing through economic and other supports where the institution of marriage has seriously weakened and cohabitation has become common. But even in nations that have the most extensive welfare measures, such as the Scandinavian countries and France, a substantial gap in child wellbeing remains between those children who grow up in intact families, and those who do not… all the evidence we have shows that individuals fare best, both in childhood and in later life, when they benefit from the economic and emotional investments of their natural parents who reside together continuously and cooperate in raising them.” Popenoe, D. 2009. Social Science and Public Policy. Vol 46, Number 5, pp. 429-436. 
  http://www.springerlink.com/content/h155411803161mv5/