The "pet theory" is that Lev 16, Lev 5, Is 53 and 1 John 2:2 are all in agreement as is 2 Cor 5:21. (I suspect we agree more than we differ here - but your wording strikes me as unusual)
2 Corinthians 5:21 God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.
This is an extremely important verse to show imputing our sins to Christ, so the imputing of righteousness to man seems logical, BUT:
Is that even a good translation?
What does “Christ made to be sin” or “Christ made sin” mean: did Christ become a sinner, did a being become an intangible thing like “sin” and are there other scripture to help us with this?
If you go to the NIV there is an alternative translation for at the bottom where “sin offering” is given as an alternative to “being made sin” and we all know Christ was a “sin offering”, so what support is there for that translation?
Paul being a scholar of the Torah, used a Hebraism. In this case, the Hebrew word for "sin" was also used to mean "sin offering" (see the Hebrew word: chatta'ath), and thus to be "made sin" was a Hebrew way of saying "made a sin offering". the NASB cross-references to Romans 8:3 which uses "sin offering" in a similar text as 2 Corinthians 5:21
There is the analogy in 2 Corinthians 8:9; the cross-reference to the clearer statement in Romans 8:3 that Christ was sent "in the likeness of sinful flesh" to deal with sin; and the allusion to Sacrifice in 2 Corinthians 5:21 where it says Christ "knew no sin" in corresponding to the sacrificial animal being free of blemish (otherwise Paul saying "knew no sin" would be irrelevant here).
The Greek word for "sin" that Paul uses is used in the Greek Old Testament both to mean "sin" and "sin offering," with both usages even in the same verse such as in Leviticus 4:3.
You can certainly do a deeper study of 2 Cor 5: 21 and we can go into Ro.3-4.
Lev 5:6 He shall also bring his guilt offering to the Lord for his sin which he has committed, a female from the flock, a lamb or a goat as a sin offering. So the priest shall make atonement on his behalf for his sin.
The offering is definitely “for his sin”, but the offering, which can be a bag of flour, is not to take his place. The atonement process is completed with the burning of the offering and with that out of the way God forgives.
Rom 6:
What shall we say then? Are we to continue in sin so that grace may increase? 2 Far from it! How shall we who died to sin still live in it? 3 Or do you not know that all of us who have been baptized into Christ Jesus have been baptized into His death? 4 Therefore we have been buried with Him through baptism into death, so that, just as Christ was raised from the dead through the glory of the Father, so we too may walk in newness of life. 5 For if we have become united with Him in the likeness of His death, certainly we shall also be in the likeness of His resurrection, 6 knowing this, that our old self was crucified with Him, in order that our body of sin might be done away with, so that we would no longer be slaves to sin;
Yes, we get the full sense of our burying our old life of sin and rising to a new life (baptism is the physical experience we have to help us realize what is happening to us spiritually).
This verse does not say: “Christ was crucified instead of us or took our place”, but says: “our old self was crucified with Him”, so how do we experience that painful torture, humiliation and murder? Did God the Father while in heaven (or at His side) empathetically experience the crucifixion? Did you empathetically experience being crucified with Christ when you came to Love Christ?
Gal 3:
13 Christ has redeemed us from the curse of the law, having become a curse for us (for it is written, “Cursed is everyone who hangs on a tree”), 14 that the blessing of Abraham might come upon the Gentiles in Christ Jesus, that we might receive the promise of the Spirit through faith.
The Greek words translated “for” in this place and most others times meant: “because of” or “as a benefit to”. The Greek word “anti” used 22 times in scripture can mean “instead of”, but also can mean: “because of” or “as a benefit to”, but that is not used here.
What Christ did on the cross for our benefit and because we sinned, was harsh in every way, which should bring us to our knees, if were not for the fact the greatest Love is being shown us at this time.
2 Cor 5:21
21 For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him.
Explained above
1 Pet 2:
23 who, when He was reviled, did not revile in return; when He suffered, He did not threaten, but committed Himself to Him who judges righteously; 24 who Himself bore our sins in His own body on the tree, that we, having died to sins, might live for righteousness—by whose stripes you were healed.
1 Pet 3:18 For Christ also suffered once for sins, the just for the unjust, that He might bring us to God, being put to death in the flesh but made alive by the Spirit,
First: we need to explore the meaning of: “bore our sins in His own body”? Do you believe Christ was made a sinner? I think we do not like the idea of Christ becoming a sinner or that sins are tangible things that can be carried around, so most seem to think this has to do with punishment for sins, Christ is taking the punishment a sinned deserves or like a sinner deserves? Peter refers to Christ as being the just and doing this “for” us (again the meaning of the Greek word translated “for” is not “instead of”, but “because of” or “to benefit”).
We are the ones who have died to sin (sins are like dead stuff to us).
This does not say we have been made righteous, but so we
might live
for righteousness.
The black and blue marks (stripes) heal us (cure the disease of sin).
Who has the problem with us going before God? Does God lack the Love to accept us or do we have the problem?
Lev 5 and Lev 16 both show that the only sins atoned for - are those that had been confessed and the blood claimed. Which means confession and repentance is part of that process.
Lev. 16 is different: These are for sins you think you may or might have committed, but
are not sure if you did or that what you did falls under being a sin, while Lev. 5 talks only about unintentional sins you
have become aware of. It is hard to “confess” to a sin you do not know you even committed.
Lev. 16 is trying to help people who get paranoid about sinning and have heavy fearful guilt, thus they start worrying about just the possibility they might have sinned.
But the mechanism/benefit comes from the substitutionary atoning sacrifice of Christ - plus His mediatorial work as our High Priest in heaven as we confess and repent and appeal to His work in our behalf. All of it is needed for our atonement to be complete.
What is completed "at the cross" is the "Atoning sacrifice", not the entire Lev 16 process of atonement.
Peter gives the best “Christ Crucified” sermons the audience in Jerusalem at that time could have, so why did Peter never talk about the benefits of Christ taking their place on the cross? Peter really emphasizes their murdering the Messiah, which cuts them to the heart (the worst feeling they could experience without dying themselves [they experienced being crucified with Christ]).
Any wonderful parent will not only quickly forgive a disobedient child, but, if at all possible, will see to the fair/just Loving discipline of the child and will also experience the harsh pain with them to further build the relationship, so is God a wonderful Parent?