I know enough about genetics to know that, eventually, inbreeding is a genetic dead-end. Father/daughter procreation, if occasionally in the gene pool, isn't as dangerous as is popularly claimed. But, parent/child procreation more than one generation gets the chances of genetic error climbing exponentially. Livestock farmers know this only too well. Apply the concept to humans, then.
Sex and Society? The problem with society is its basic premise. Crowds of easily misled people are better at controlling society than intelligent, educated others. This, of course, is stupid. That's society for you, though. Stupid.