While Kevin Smith's argument isn't doing the position much credit, there are some good reasons to keep Lex white, especially since they seem to be going with the Post-Crisis interpretation (LexCorp references). If Clark/Superman represents the best of America's past and what it "used to be" (small town values, optimism, hardworking, independent), Post-Crysis Lex represents the worst of modern America and the flip side of the aforementioned virtues - selfishness, self-importance, corporate greed and influence, cynicism and the like. In those attributes, the Post-Crisis version of the character is extremely topical and relevant and, to be fair, the imagery of corporate America and white collar crime is white males. If superhero comics are modern popular mythology, then it is largely fair to say that the major character are archetypes.
Making Lex an racial/ethnic minority dillutes the character archetype of the arrogant, white corporate crook that he could represent. Especially if Lex is portrayed as outwardly virtuous and beloved, but inwardly corrupt. Then, it is arguably more interesting if he outwardly appears to be a charismatic, all-American white male type who isn't what he appears when the illegal immigrant/alien character of Kal-El, who is casting aspersions on as foreign and not be trusted, actually is because he was raising by the right people.