"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 convincing. The author does not provide a reason 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:
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. The author's tampering with the biblical doctrine of the atonement is dangerous.
What is the way that God reconciled us? How did He do it? That is what the Apostle Paul is talking about. Therefore, a forensic-imputation theme completely fits with the flow of Paul's message. He is making the appeal precisely because of the reality of imputation. That is the very reason we may be reconciled to a holy God. So, Catholic Nick's argument does not stand up at all.