You and others keep talking about the fall as if it were anything other than Adam sinning. There is no statement about the fall of the world anywhere in scripture.
It is true the Bible does not contain the exact phrase "
the world fell into sin," but the premise of the "
fall" is not speculation (the forming of a theory without evidence). 1 Timothy 2:14 plainly states Eve "
fell" into transgression. Therefore, anyone who has sinned could be said to have "
fallen" into transgression, or fallen into sin. There's nothing speculative about that; it is a reasonable and rational generalization based on something explicitly stated in scripture. Similarly,
Romans 8:20-21 states the creation was unwillingly subjected to futility and needs to be set free from the slavery of corruption. We might ask ourselves, "
What corruption?" since according to Genesis 1:31 God made the world good (and sinless) but that question is easily answered because the Bible repeatedly draws a parallel between sin and corruption. Peter states the world is corrupted and attributes the corruption of the world to "
evil desires" (2 Peter 1:4). Very early on in scripture the Bible states, "
God looked on the earth, and behold, it was corrupt; for all flesh had corrupted their way upon the earth" (Gen, 6:12) and whether or not that corruption is attributed to sin or sinful humanity the fact is the entire world became corrupt. Notice also this is another verse that explicitly states the flesh had become corrupted.
The point being this is not speculation; it is
inference.
Whether or not the corrupting effects of sin were instantaneous (following immediately due to Adam's disobedience) or gradual (resulting from the cumulative effect of every human sinning) the result is identical: a corrupted earth. Romans 5 tells us that through one man's disobedience sin entered the world. It entered the world, not (just) Adam, and not (just) the garden. Sin entered the
world. So, again, we can point to scripture that states sin entered the entire world and the entire earth is corrupted, and the Bible attributes the entrance of sin into the world to human desires and one man's disobedience. Those are the stated facts of scripture, not speculation. They're not inference, either. The inference comes when we take the fact one man's disobedience caused sin to enter the world and we attribute that act to the subsequent death that Romans 5 states came (past tense) to all men because all sinned. The passage does not explicitly state Cain, Abel, Seth, or and other subsequently born human being became sinful because of that one man's disobedience. We generalize sin's entrance into the world and sin eventually corrupting both the entire earth and human flesh because of what is stated. We
infer that because scripture has already stated sin corrupted the earth and all flesh. The corruption is not speculation. When scripture speaks of the whole of anything that, logically, includes all of the constituent elements of that whole thing. So, when the whole earth is corrupted that necessarily means, logically speaking, all the constituent components of the earth are corrupted. That would include humans (since there are no non-earthly humans). That is a deduction, not an inference, and definitely not speculation.
I will concede (for the moment) Genesis 6:5 contains a certain degree of hyperbole but, putting aside the hyperbole, the verse still plainly states
the wickedness of mankind was great on the earth, and that every intent of the thoughts of their hearts was only evil continually. So, imagine what a child born into a sin-filled world in which every human intent and thought of the heart was only evil all the time. How long would it take for a pure, unadulterated, uncorrupted child to be affected by the abject corruption into which his birth immersed him? Therefore, when Psalm 51:5 states, "
Behold, I was brought forth in guilt, and in sin my mother conceived me," we might read that to say it is an innocent, sinless child but that inference does not accomplish much because that child is immersed in an inherently corrupted (sinful) world to be raised by two (or more) sinfully dead and enslaved sinful parents. The second either parent pours a word of sin into that child that child has become corrupted. This is one of the reasons why the solution had to be a birth that was not of sinful will or sinful flesh. Those who receive Christ are given the right to become children of a different kind, children who are not born of the blood, the will of the flesh, or the will of man. They have the right to be born of the will of God. The blood, the will, and the flesh are (all three) problems to be solved, not the solution or the means of obtaining the solution.
All of this is attributed to the disobedience of one man, and that one man is Adam. If Adam hadn't disobeyed God, then sin would never have entered the world. If sin had never entered the world, then no one would be dead in sin. If Adam hadn't disobeyed God then he would not have become sinful, a sinner, or a sinful sinner. His flesh would never have become corrupt and sinful. His will would never have become corrupt or sinful. Had he never disobeyed God his behavior would not be sinful (this is axiomatic). All of the same holds true for Eve, too. Scripture plainly states she "
fell" into transgression and became a sinner.
Therefore, there is an exegetical basis for using the word "fall," and saying there was a "fall" into sin in which the entire earth became corrupted by sin's entrance. I, personally, don't often use the word "
fall" when discussing sin. I don't use "
spiritual death," either. I don't use "
dispensation," or "
covenant of works," and many other doctrinal terms when the words of scripture serve best, either. Drives folks nuts. I try to use the language of scripture. I, therefore, fully embrace the basic point of your protest, but it won't go anywhere as long as why the term is used is avoided. It's not that inferences are inherently or automatically incorrect or because they are something to be avoided, because
some inferences, those that are built on what is explicitly stated, are valid and veracious, while others are not. The use of inferential terms becomes unnecessary when using the language scripture uses. Everyone reads scripture inferentially to one degree or another. The question is whether or not and to what degree the inferences are exegetical versus eisegetical.
People are dead in transgression. Period. Nothing more needs to be added. What is sin? Sin is any missing of the target God has set for His created creatures, and in the case of humanity that target is perfection, righteousness, faith and faithfulness, and obedience;
not just the last definition, obedience. Defining sin
only as lawlessness is myopic and therefore unscriptural. And that is where the sin-is-only-lawlessness argument fails. The word "
only" does not appear in 1 John 3:4. Any lawlessness is sin because sin is lawlessness, but sin is not
only lawlessness. It is speculation to insert the word "only" into 1 John 3:4, not inference. It is speculation to inject volition into any verse where the word is not stated, and the context does not permit. It is, likewise, speculation to inject determinism into any verse where it isn't reported in word of context.
For the above reasons and based on the many verses cited above, the "
fall" of the world into sin is not speculation; it is inference.
. One person says, "You're an X," and the other says, "No, you're Y," and the two have accomplished nothing. If, however, someone makes a factual statement, and that fact is found confrontational then it is not the messenger that is the problem. If I am, in fact, a dunderhead, then I don't like that but it's not the messenger that is the problem. 
. We all know the terrain here. We're at our best when we form our case with well-rendered scripture, not when we feel put on the defensive. Big hug. Now....
