Given that various organizations like the Ku Klux Klan and the Confederacy have historically used religion to justify segregation, their idea of “sin” is radically different from those who fought for equality and fairness.
The pool players singing sin can therefore be read as them fighting against what their oppressors would have seen as righteous actions and their “sins” are therefore acts against authority, not necessarily immoral in the sense of violating a higher morality. The next line says the pool players “Thin gin.” Gin is historically a spirit associated with both the very poor and the upper class. Assuming “thin” is being used as a verb, the pool players are therefore ruining something that affects all classes of people. Racism and segregation are not problems that are limited to socioeconomic
status. This pattern of double-meaning and word play all allow the pool players to be portrayed as more than just wayward youths; they are criminals in a world where doing the right thing is considered wrong.