That's a bit of a non-sequitur. In truth, I don't see anything obviously sexually deviant in being a swinger; "swinger" is really just another word for "promiscuous" when you get right down to it. They weren't homosexual, and there were no farm animals or underage people involved. The difference between them and the average promiscuous American is that they are honest about it.
I don't really find the lifestyle to be savory, but I don't think that it is much of a sexual deviation as they were doing it either. I've known some otherwise upstanding individuals who did swing on rare occasion, some of whom are far more conservative than I am; most do not make it an overt lifestyle and you generally would never know unless you were told. Different strokes for different folks I guess. I don't really consider it an issue unless a person makes it a problem. As I said, I've never done it and kind of look upon the practice with some distaste, but I don't see it as an innate social problem either.
Granted, these don't seem to have been the most responsible parents, but that has very little to do with the fact that they were swingers. There are vast quantities of equally irresponsible parents who don't have "sexually deviant" proclivities who it could have happened to.
If you go shopping in the sewer, you won't find angels. Lifestyles mean a lot. Sexual deviants shouldn't have children to corrupt.