Gay marriage is really an issue of principle than of percentage. I know I'm the millionth person to say this, but if gay marriage is legal, why not incestous marriage, polygamy, etc.? Isn't their age of consent for sex quite low too?
Check out this link for "Voor een verloren soldaat" (1992)
a mainstream Dutch film that romanticizes man/boy sex.
www.imdb.com/title/tt0108504/
And the question about principle is whether it is a matter of state to impose principles. The Dutch have decided that it is not. They can tolerate gay marriage. Does that make them all liberal and decadent? They don't seem to be to me.