Well, their population WILL decline but since only 1-1.5% of people CHOOSE homosexuality, the decline will be minimal.
What is appalling is their CHOICE to put the sin of homosexuality on the side of RIGHT. It is an abomination in no uncertain terms.
They WILL repeat the rewards of condoning Satan's bailiwick.
I disagree, for two reasons:
First, the embrace of homosexuality is a tail-end indicator of a general rejection of natural reproduction. Before a society approves homosexual "marriage," a sufficient percentage has already decided that national extinction is acceptable.
Secondly, the choice to engage in homosexual activity is strongly affected by the society's values. There was nothing genetically peculiar about the men of Athens or Sparta: they simply preferred man-on-man sex, for a number of socially-driven reasons.
When enough people in a society pursue genital pleasure independent of permanent, procreative families, the sex of the sex-partner quickly ceases to matter. For example, a man who is used to performing sodomitic sex acts on women can easily switch to a man, if that's all that's convenient when he wants to do it.