He is past redemption. Within what is possible in the type of story Mashima wrote, going from A (Gajeels crime) to B (His romance with Levy) cannot be done.

I'm not ignoring what you brought up. If that stuff was in there, I have nothing to refute and you're right. But it also doesn't matter. You have a point that his switching sides is nothing unusual, and done well, but that isn't the specific part I have a problem with.

I said that these series gloss over some things because they are told superficially, but that also makes certain turns impossible without turning off your reader.

One such turn this series attempts and fails to make, in pairing off Gajeel and Levy.