The concepts of clean and unclean are used to create boundaries and define identities. In his book Unclean Richard Beck explores these boundaries in terms of "disgust." Disgust tends to be socially defined or learned behavior. Thus, Western society eating bugs can be disgusting, but may not be so in other societies. Thus, in the Levitical holiness codes eating shell fish or pork is an abomination -- that is, it's disgusting. Beck notes that much of the discussion of disgust has to do with food or things we put into our mouths.
Sociomoral disgust takes this boundary defining concept and applies it to human beings. The Jew/Gentile divide is one of those boundaries. Jews and Gentiles looked at each other with a degree of disgust. Sociomoral disgust leads people to see others as contaminants, and this can lead to violence and genocide.
Sociomoral disgust can extend, on a case-by-case basis, to individuals we deem “disgusting,” “revolting,” or “creepy.” We make these attributions for a variety of reasons (e.g., poor hygiene, moral failures). Regardless as to the source of the attribution, we experience feelings of revulsion in proximity to these people.
Further, sociomoral disgust can apply to entire populations. Racists tend to view the despised group as a source of contamination. This happened in America with the slave population and in Nazi Germany with the Jewish population. But these are hardly the only examples. Wherever hate, racism, or genocidal impulses exist, sociomoral contamination and disgust take center stage. [Richard Beck, Richard, Unclean: Meditations on Purity, Hospitality, and Mortality (p. 74).]
And Jesus, following the lead of Hosea (6:6), in Matthew 9, declares that God prefers mercy to sacrifice. That is, mercy over purity. Beck writes:
The problem was that a class of people—“tax collectors and sinners”—were understood to be, intrinsically, a form of pollution. Strongly, these people were waste, contaminants, vectors of contagion. Thus, contact with these persons was prohibited if one wanted to maintain a stance of holiness and purity. [Beck, Unclean (p. 75)].
In Acts 10 Peter has a vision in which God declares certain foods that Peter as a good Jew would never consider eating to be clean, and then that vision opens his eyes to the new status of Gentiles.
The question that we must ask is this: Who do I view with sociomoral disgust? Who is the other that I seek to separate myself from and what steps am I willing to take to erect the boundaries or remove the perceived contaminant from my midst?