This excerpt will give a flavour of what Peter Berger is saying:
"Conservative cassandras (please note: I am not one of them) are turning out to be empirically correct, even if one disagrees with their philosophy: once you legitimate same-sex marriage, you open the door to any number of other alternatives to marriage as a union of one man and one woman: polygamous (an interesting question for Muslims in Germany and dissident Mormons in Arizona), polyandrous, polygenerational – perhaps polyspecies? Our Hamburg trio may well be correct in their expectation that polyamory may be the wave of the future. (Actually, the term could be expanded to cover all the above poly-arrangements.)"Speaking, I suppose, as one of them, there's only one problem with the term 'Conservative cassandras.' I'm sorry for being classically pedantic here, but isn't the main thrust of the myth that Cassandra herself turned out out to be "empirically correct" in her own original predictions? The curse laid on her by Apollo was that no one believed her.
Does that ring any bells?