Rashi comments that the ultimate verdict for the destruction of that generation was based upon the people’s stealing. The Ozorever Rebbe, z.l., explains that the arrogance demonstrated by the manner of this stealing signified a decadence so sinister that repentance for this sin was highly unlikely. Their form of stealing was unique in that it was not biblically prohibited, since the people were careful to steal less than the value of a “perutah” (which is the criterion for establishing an act of stealing). They obviously derived no benefit from such an insignificant theft. They stole for the pure sake of stealing; they sinned for the thrill of sinning. They seemed to be noble and dignified people who diligently researched the law, seeking loopholes to enable them to accomplish their immoral acts within a legal framework.
Such an attitude could never lead to repentance. What did they do wrong? They were able to find the proverbial “heter”, permission, for their miscreancy. He interprets the pasuk in the following manner: “And the earth was corrupt before Hashem,” but Hashem is aware of an individual’s true intentions. It was the fact that they sought ways to legally steal (with permission) that sealed their destruction. One who sins “only” before Hashem will be punished before man.