When my father once brought up the "gay downfall of Rome" hypothesis, I pointed out that it made much more sense to blame the downfall of Rome on the Christians. After all homosexuality had been celebrated in Rome for centuries, but it wasn't until the Empire became officially Christian that things fell apart completely.
as there isn't yet a Wacky Things Immigrant Parents Believe list...
certainly in the Balkans the gay mafia theory is not unheard of, and friends let me know that their immigrant parents entertain similar notions. my father is quite a one for putting a little lemon-slice of crazy onto notions already ludicrous. to wit, he has stated firmly several times that Persia and Rome fell because of The Gay...somehow.
(his repertoire also contains the gay anti-smoking conspiracy, whereby North American doctors have been bankrolled by the rich, powerful gay government infiltrators to spread anti-smoking propaganda...for some reason)