1. The Doctrine
Hereditary Total Depravity is not as you say, "the Biblical expression of the effects of sin on human nature." On the contrary, it is the effects that Adam's sin allegedly had on human nature.
You write, "HTD does not mean that every person is as bad as they can be." Well, the Reformed Creeds disagree with you.
So, man can choose what to eat, where to go, and what to wear, but he cannot choose righteousness? Good news? Never! The gospel according to Calvin is a bouquet of barbed wire.
In truth the effects of Adam's sin did not rob man of his free will in matters of salvation. The Holy Spirit continually offers man salvation choices (Dt 30:19; Jos 24:15). Jesus said, "You are unwilling to come to Me so that you may have life" (Jn 5:40). Obviously, Jesus was not a Calvinist. The gospel says, "God so loved the world, that He gave His only begotten Son, that whoever believes in Him may not perish, but have eternal life" (Jn 3:16). The "whoever" is anyone who wishes (Rev 22:17). This is the word of the Lord! God be praised!
2. The Fall
Yes, God had warned Adam and Eve (Gen 2:17). But they high-handedly disobey God, the result was both died spiritually that day, and sin entered into the world. God drove them away from the tree of life. Adam and Eve no longer had anything to sustain their physical bodies indefinitely. From that day the long slow process of deterioration eventually led to their demise. When Adam was barred from the tree of life, we (his posterity) also lost access to the tree of life (Gen 3:22-24). In this way aging and physical death passed to all his descendants. As the Scriptures say, "in Adam all die" (1Cor 15:22).
I did not personally eat the forbidden fruit. I am not guilty of Adam's sin although I suffer the consequence of his sin. Let me illustrate, in Dublin Ireland there was a child happily playing on the footpath of the street in front of her house. A car driven at speed by a drunken driver turned into the street, as he turned the corner the drunk driver lost control. The car mounted the pavement and pinned the child to her own garden wall. Her injuries were horrendous and as a result she died. Question: was the child guilty of drunkenness? Obviously not! But had she suffered the consequence of the man's drunkenness? Yes she had! It is only because Adam is the father of the race that "the many" (all) die as a consequence of Adam's sin. Paul's argument is we die whether we sin in the likeness of Adam's sin or not, that is, whether our sin had a death penalty attached to it or not.
Micah you say, "they (Seth/offspring) were fallen, no longer good," if they were no longer good, they were bad. It stands to reason, if they were bad (as per the doctrine of HTD), then they no longer had the image of God.
In Romans 5:12-21 Paul uses Adam, as a type of Christ. But Adam was not a saviour was he? No, he is only a type of Christ because he is the federal head of the human race (physically), while Christ is federal head of the human race (spiritually). In Micah's interpretation Jesus has a lesser headship. For Adam is head of the whole race but Jesus is only head of the elect. This restricted headship does not fit the scope of Romans 5.
When Adam sinned he brought sin and death into our world. This curse and the other curses in Genesis 3 were unconditional. They are in the world despite what we do or don't do. "Through one transgression there resulted condemnation to all men." The condemnation is "For you are dust and to dust you shall return" (Gen 3:19). In Adam every human is cursed to die physically.
"While through the obedience of the One many (all) will be made righteous." The same "many" who are condemned in Adam, will be made righteous in Christ – righteous to the degree that the curse of death has been removed from them. That means all men can be raised from the dead. Micah believes; Adam's condemnation (physical death) extends to all men, while Christ's justification is restricted to "His people, the church." That is not what Paul is teaching. He is saying that in Adam "the many" (all) die while in Christ "the many" (all) are provided a "justification of life" unconditionally. This "justification of life" counteracts Adam's sin; so all men can be raised from the dead (Rom 5:17-19). However, Christ's death covers "much more," than Adam's transgression, it also covers the "many transgressions" of all men. Of course, only those who want of "the abundance" will receive the "free gift of righteousness" provided in Christ's death (Rev 22:17).
Micah argues that death in Romans 5 is both physical and spiritual. Then as night follows day verses 18-19 teaches, "all men" die and "all men" receive "justification of life," that is universal salvation!
3. Dead in sin
Micah understands that the slave of sin is one who “commits sin” (Jn 8:34). Jesus was talking to His contemporaries, people who believed in Him, who were commanded to abide in His word. So this verse too teaches that actual commission of sin is required for one to be alienated from God.
We are spiritually dead in sin not because we are born that way, but because we choose to live in sin. Psalm 58:3 teaches people were old enough to speak lies. "They have gone astray" is not synonymous with born astray.
"There is none who does good" (Rom 3:9-10). The explanation is in the verse read on, "all have turned aside, together they have become useless." It does not say, all were conceived astray and born useless. So this passage does not prove HTD either.
"Walking" means living (Eph 2: 3, 4:1; 5:2). Formerly, under the influence of Satan, these Christians had lived in disobedience to God. They were dead in their sins because they had chosen to live that way. The word "nature" as it is used in this context is used, not of birth but of "long habit" (Thayer, Greek-English Lexicon, 660). Yes, these Christians by living in sin and practicing sin were depraved. There is nothing about being born dead.
Micah, the word "sick" is used by Jesus to describe the spiritual condition of sinners (Lk 5:31-32; Isa 1:4 -6).
4. Unable to please God
"But the natural man does not accept the things of the Spirit of God." The natural man is described in Romans 8:5, "For those who are according to the flesh set their minds on the things of the flesh." The natural man is a description of a mind-set. These people look to nature, and the wisdom of man for answers to life. The fleshly minded mistakenly believes there is nothing beyond what he sees, hears, tastes, smells and touches. King Herod, Pontius Pilate and in our own day the evolutionists like Richard Dawkins, and many humanists are typical of the natural man.
A person like this does not accept the things of the Spirit (the gospel), for they are foolishness to him. The things of the spirit world can only be appraised spiritually, that is by the revelation of God. Because the natural man refuses to be guided by revelation, he rejects God, Christ, redemption, heaven etc. These things are nonsense to him. Preaching Christ crucified was to the Jews a stumbling block and to Gentiles foolishness (1Cor 1:23). So, faith was impossible for them.
The people effected by the "natural man" syndrome range from the naive youth to the College Professor, from the immature Christian to the Atheist. However, God is putting constant pressure on the natural man to give credence to the spiritual world. God has set eternity in his heart (Eccl 3:11): The evidence for God is within him (Rom 1:19). The glorious creation witnesses constantly to the Creator (Rom 1:20; Ps 19:1). Even the futility of life plays it part by coercing the natural man to look for something better (Eccl 2:11). Combine these subtle pressures with circumstances that rock the natural man's world, and his unbelief can turn to faith. Remember the Ninevites! (Jonah 3:5, 10) Ordinarily, the natural man is unwilling to come to Jesus (Jn 5:40), but that mind-set can change, as the case of the Corinthians, and the Ephesians proves (Eph 1:13-14).
"For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek" (Rom 1:16). Still, the gospel must find a willing heart (Jn 7:17).
The doctrine of Hereditary Total Depravity contradicts the Scriptures. A man cannot inherit his father's sin nor his guilt nor his punishment (Ezk 18:20).