We have values that respect the production of offspring (tax credits just for procreating come to mind), and crowded Europe does not.
Show me some path of causality between homosexual marriage, and imploding birthrate, and I'll believe you. And none of this nonsense about having an FMA will encourage homosexuals to go straight, marry and have kids. That would work about as well as Prohibition abolished drinking.
It is a characterization, ala the economic freedom index vs GDP published in the WSJ.
You will not find a hard generalization/causation.
It is sort of like are upper class people that way because they went to good schools, or do they do to good schools because they are upperclass.
btw, france put in income tax incentives for kids...
Also, those very values you mentioned would be tossed, since gay couples will the state to take away kids from 'abusive (eg discipline)' parents and get same credits!