It should not be : I have grace so I do anything I want.
Rather: I have grace so I do everything God wants.
You know the grace of God ensures that what you want is what He wants?
This extends to service. Peter said that we should be stewards/ channels of the manifold grace of God in our service. I bet your grace confusionist did not link grace to service, just to rubbish.
Did he tell you manifold means many-sided and that the grace of God is many sided? So how has he been able to get away with preaching only one side? That smells like deception.
The many sides are not determined by the imagination of the speaker, but what the Scriptures say. Or is it not the same Bible with the 66 books we are talking about?