I wouldn't say that Harf is dumb; rather, she and others like her have had their consciences "seared" (as is cauterized) to the point of moral insensibility. These people cannot admit to the existence of moral absolutes because if they did, then they would have to reckon with their own evil.
God has given them over to their wickedness, as Paul wrote in Romans. There but for God's great grace and mercy go I.