That is a critical point of differentiation - while many supporters of homosexual marriage might demur to the characterization, it is clear to me that a major impetus behind their efforts is their hatred for traditional American society and culture, and their resultant excitement at the prospect of damaging it, step by step, in a long march towards its destruction. (Although I should in fairness state that not all such proponents fit that broad-brush characterization - there is certainly a libertarian argument which can be made that differs from the nihilistic approach that permeates much of the discussion favoring gay marriage). Which leads me to believe that a doomed society is in fact their unstated goal. Those who believe in "living in a healthy and vital society with a long-term future" may find it hard to understand the goals of the "doomers", but they should remain vigilant against them...
I too liked that quote. The strongest arguement to a person who asks "How does homosexual marriage, or homosexual normalcy harm you?" It is clear that it may not harm specific individuals. Some of us are well past the age that homosexuals target for recruitment. But we can still see that the society that they want to emerge and florish is not a society that holds enough morality to survive. We have to be firm about this. Even to the extent that we support a constitutional ammendmant.