Final answer:
The referent for "it" in Perry Smith's phrase regarding the Clutters typically relates to a severe consequence or act of retribution that the Clutters endured, possibly alluding to the murders detailed in 'In Cold Blood' by Truman Capote.
Step-by-step explanation:
The referent for "it" in Perry Smith's statement, "The Clutters were the ones who had to pay for it," is referring to the consequences or retribution for some unspecified action or event. Since the statement lacks context within the question, "it" could imply a punishment or unfortunate outcome that befell the Clutter family. In historical context, this statement could be associated with the infamous murder of the Clutter family in 1959, which was later chronicled by Truman Capote in his book 'In Cold Blood.' Therefore, the 'it' that the Clutters paid for could be interpreted as Smith's perceived justification for his actions, which tragically resulted in the murder of the Clutter family.