Bumping this to get some commentary going, but I have to say the author could use a logic course. It may well be true that it is always immoral to separate the unitive and procreative elements of sex. Indeed, volumes have been written on it. It may well be true that birthrates have fallen precipitously among non-muslims (and apparently is true in Europe, though not necessarily elsewhere). And the separation of the procreative and unitive aspects of sex may well be a factor in some regions - probably is, in fact.
Nevertheless, effect B (lower birthrate in Europe) is not "empirical" proof of premise A (the immorality of, for example, contraception), because if every couple banged out three kids THEN practiced contraception, the argument falls apart. Yes, it may still be immoral (count me in among post-1930 Protestants in this regard, though), but there are much better arguments for this premise than the "empirical" evidence cited. The author would be better off simply arguing that "we need more kids" based upon the data provided.
Just realized you re-posted with paragraphs. I'll re-post my comments there (pre-paragraphed).