Sforno on Genesis 18:23/ספורנו על בראשית י״ח:כ״ג

1האף תספה צדיק עם רשע, Avraham felt that the way G’d had worded the decree with the word כי רבה, that what G’d might have meant was that as long as the majority of the people were guilty this would justify eliminating the entire city, including the innocent. In that event G’d would not be perceived as meting out justice.