How does Rubin present the notion of sexual hierarchy in the book?

The major theme of “Thinking Sex” is that American society always organizes sexual acts into a hierarchy. That means it values and legitimizes some sex, usually heterosexual intercourse in marriage. Any sex that is different than this is lower in the hierarchy, and the more different it is, the lower it goes. For instance, homosexual sex that is in a committed relationship will be higher on the hierarchy that homosexual sex that is casual. Unfortunately, progressive movements also create hierarchies in order to legitimize themselves. Thus, gay rights activists that advocate for a higher spot on the hierarchy might commit to a form of “respectability politics” in which they hold up some kinds of gay sex as being better than others. Sadomasochism, for instance, might be stigmatized in order to make "caring" sex within a committed relationship look better by comparison.