"First, the text does not suggest we become righteousness in the same way Jesus becomes sin, i.e. by a double imputation, because Paul uses two different Greek words here, "made [sin]" and "become [righteousness]."
Just because someone references Greek, does not mean that his or her argument is valid or convincing. Nick fails to explain why the two different words necessarily rule out imputation.
If Roman Catholic infusion is correct, then should we conclude based on 2 Corinthians 5:17-21 ("Christ was made sin") that the essence of Jesus was corrupted? Was evil infused into Christ?
"Second, the curious phrase "made sin for us" cannot be presumed to include Christ's perfect obedience to the Law, especially since the Protestant says this phrase refers specifically to having our sins imputed to Christ."
What does it mean to say that Christ was made sin for us? Dr. Ron Rhodes has some pertinent observations here:
This point is invalidated because of the background of the Old Testament sacrificial system, which is all about the transfer of guilt. Look at Genesis 22, Leviticus 16, and Exodus 12. In all three instances, there is an innocent substitute provided. The lamb died in the place of a person, etc.
The meaning of 2 Corinthians 5:21 is crystal clear. Jesus took our sin and gave to us His righteousness. We do not deserve His righteousness, anymore than He deserved to bear our punishment. That is the legal, binding transaction which takes place in the "court" of God. He has voluntarily paid an infinite sin debt on our behalf because of His love for us. He saved us because He is gracious. He is our sin offering.