Fatal Flaw Bump.
I agree with your identification of the "Fatal Flaw" in that it agrees with God's Word regarding our inherent nature:
Sin entered God's perfect world when Adam and Eve gave in to the temptation offered by the Serpant, Satan. Since then, all mankind is born in sin - (Psa 51:5 NKJV) "Behold, I was brought forth in iniquity, And in sin my mother conceived me."
All men, since the Fall into sin, are spiritually dead in sins - (Eph 2:1-3 NKJV) "And you He made alive, who were dead in trespasses and sins, {2} in which you once walked according to the course of this world, according to the prince of the power of the air, the spirit who now works in the sons of disobedience, {3} among whom also we all once conducted ourselves in the lusts of our flesh, fulfilling the desires of the flesh and of the mind, and were by nature children of wrath, just as the others."
In our fallen state, we are inclined ONLY to evil - (Gen 6:5 NKJV) "Then the LORD saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually."
(Gen 8:21 NKJV) "And the LORD smelled a soothing aroma. Then the LORD said in His heart, "I will never again curse the ground for man's sake, although the imagination of man's heart is evil from his youth; nor will I again destroy every living thing as I have done."
(Rom 8:7 NKJV) "Because the carnal mind is enmity against God; for it is not subject to the law of God, nor indeed can be."
In addition, there is a fatal flaw of logic in the statement (highlighted by bold text). If man is inherently good, how can he be depraved by society that is made up of "inherently good" people?