As an orthodox Protestant, I advocate and defend the doctrine of justification by faith alone as the standard against all false expressions of Christianity. And the consistent response from advocates of works righteousness is almost always that it means that a person can believe, and then live however wickedly he wants, and still be saved. They usually cite James 2:24 (an objection which I address here). I get this supposed trump-card most consistently from Mormons and Catholics.
Their claim is a caricature. Worse, it is a slogan, repeated from some apologetics book or class, not something thought through by the person making the accusation.
It is easy to refute. I have provided one such refutation in the link above. Another is found in the little epistle of Jude, especially verse 4: “Certain people have crept in unnoticed who long ago were designated for this condemnation, ungodly people, who pervert the grace of our God into sensuality and deny our only Master and Lord, Jesus Christ.” Jude here describes people who profess to be Christians, but are then involved in some unspecified sin. But notice what else he tells us about them, that they are “condemned” as “ungodly.” So, they do not have faith; they have a label. And that is a denial of Jesus, not faith.
This should be an indication to anyone who has been taught this as an argument against justification by faith that it is an accusation based on something that the Scriptures say is impossible. That means that the argument is false.
Then a far more important question should come to mind: If my religious teachers have taught me this falsehood, what are they trying to keep me from seeing as truth? They want to keep you from understanding justification by faith alone because that makes you dependent on Jesus alone, instead of them.