Paul is making a generalisation about the saints and sinners. The pure-minded Christian looks for and finds the good in everyone. This obviously does not mean that God's people will label adultery, sinful conduct, or impurity by the term "pure." On the contrary, the Word of God pronounces a curse on those who equivocate and vacillate on matters of right and wrong. "Woe unto them that call evil good, and good evil." Isaiah 5:20.
Paul portrays the defiled sinner as one with a darkened mind and conscience who makes something evil out of the pure and good. Such men lived in the days of Noah and of Paul, and they still are found in the earth. Says the Bible, "Every imagination of the thoughts of his heart was only evil continually." Genesis 6:5.