Hi 12 Strings, I do not think your "nearly every biblcal and language expert agrees" statement is valid. If you read the commentaries of Barnes and Clark, they present well studied views in total agreement with me. Remember the concept concordance. Over 90 times that same word is translated sin offering or offering for sin in the Septuigint. Which is to say a Hebrew word or phrase, which is translated into English as sin offering or offering for sin, is translated into the word found in 2 Corinthians 5:21. So a concordant translation, where the same idea is translated in the same way would read sin offering or offering for sin.
Here is the link to Barnes and others: http://bible.cc/2_corinthians/5-21.htm
It seems to me that Barnes is not here going as far as you. He does not deny that Jesus was "made sin" but rather seeks to explain what it means. He says it is either (1) he was made a sin offering or (2) he was treated as a sinner by God the Father. I would accept both of those, simply because they do not deny the actual text, which even barnes notes should stand as is:
FROM BARNES COMMENTARY:
The doctrine of imputation of sin to Christ is here, by plain enough inference at least. The rendering in our Bibles, however, asserts it in a more direct form. Nor, after all the criticism that has been expended on the text, does there seem any necessity for the abandonment of that rendering, on the part of the advocate of imputation. For first ἁμαρτία hamartia in the Septuagint, and the corresponding אשׁם 'aashaam in the Hebrew, denote both the sin and the sin-offering, the peculiar sacrifice and the crime itself. Second, the antithesis in the passage, so obvious and beautiful, is destroyed by the adoption of "sin-offering." Christ was made sin, we righteousness.
My main point is not to say Jesus what not a sin offering, or even that sin offering is not part of what is being said in this verse; but rather that I cannot say "Jesus did not become sin for us" when clearly this verse says he did. Once there, I can go on to determine what exactly that means, and rightly conclude that Jesus did not become a sinner.