The crowd at Lot's door is done bargaining. Genesis 19:9, in Targum Pseudo-Jonathan's Aramaic, records the exact accusation they throw at him.
"Did not this come alone to sojourn among us? and, behold, he is making himself a judge, and judging the whole of us. But now we will do worse to thee than to them."
Two lines, two civic sins. First, the xenophobia: this came alone to sojourn among us — you are an outsider, Lot, a single man who wandered in from Hebron, and you have no standing. Second, the resentment of moral critique: he is making himself a judge. Lot's crime, in the eyes of the mob, is that he dared to tell them their behavior was wrong.
The rabbis of the Talmud (Sanhedrin 109a) expanded this scene into a whole series of grotesque Sodomite legal practices — beds that stretched short guests and sawed long ones, courts that punished hospitality — all of them grounded in this one dynamic: Sodom hated outsiders, and it especially hated outsiders who saw through its cruelty.
Lot's situation is uniquely painful because he is both things at once. He is related to Abraham, the ultimate outsider-welcomer. And he has become a citizen of Sodom, the ultimate outsider-despiser. The mob is not entirely wrong that he is playing both sides.
The Targum's Aramaic verb for "making himself a judge" — avid garmeh dayyana — echoes through rabbinic literature as the definition of what a wicked society does to anyone who tries to name its evil.
The takeaway: the moment a community starts attacking the people who call out its cruelty, the community is already beyond saving.