I have seen evidence of society breaking down in places that have legitimatized it, but I do not know what the cause of that is. It could very well be something other than the gay marriage and likely is.
And the link (or lack of it)between these things was the point of the rest of that paragraph. If a country has made homosexuality illegal and society breaks down, then "obviously" making homosexuality illegal causes a breakdown in society. (Irony)