Of course, the article in the Huffington Post goes on to say

a) "It should be noted that the Organisation for Economic Co-operation and Development (OECD) also shows Sweden's marriage rates increasing since domestic partnership. The trend line is in the opposite direction than what the "Bishop" and O'Reilly claimed. "

b) Additionally, using the date of 2009, we see marriage rates decline and increase, with neither the highest nor lowest matching Sweden's highest or lowest marriage rates.

c) Denmark only legalized gay marriage last year, so there is no trend data.  But recognizing same-sex partnerships didn't negatively impact the rate of marriage.

d) Ditto Norway

re: Marriage

You have two options here.  Either strip marriage of all it's legal meaning and have it be a strictly religious title.  Or let it have a legal meaning and open it to all consenting adults.