And, this is exactly what Protestant doctrine does!
This is completely fallacious and demonstrates your ignorance of our doctrine. Our doctrine demonstrates that we are breakers of the law and that God is just in his judgment of us, and that we are all condemned under the law. For all have sinned and fall short of the glory of God, and are justified by his grace as a gift (note that it is not earned), through the redemption that is in Christ Jesus, whom God put forward as a propitiation (note that Christ is the propitiation, which means the satisfaction of the just punishment of our sins) by his blood, to be received by faith. After showing how we receive grace through faith, Paul continues, Since therefore we have now been justified by his blood, much more shall we be saved by him from the wrath of God. He then states that we are already reconciled with God.
The doctrine of purgatory assumes that we aren’t reconciled with God and that Christ’s sacrifice did not in fact offer the propitiation for our sins, but that we must do so through our works.
Paul even shows how he himself still struggles with sin after he is saved, but is in the continual process of sanctification. However, even then it is still Christ who has justified us. As he says, Who shall bring any charge against God’s elect (not that in God’s grace our slate is clean, we will see in a moment why)? It is God who justifies (not our actions). Who is to condemn? Christ Jesus is the one who died - more than that, who was raised - who is at the right hand of God, who indeed is interceding for us. Paul is saying quite explicitly the debt is paid. Glory to Him!
Now, that being said, the next unfounded allegation you will make is that we don’t believe in works. That would also be wrong. As Paul says, that we were created in Christ Jesus FOR good works, which he had prepared beforehand, that we should walk in them.
Again, we are saved by faith through grace by Christ, so that we can live out our original purpose.