Well stated, I really like the "devil on his shoulder" analogy. As an audience member, I agree that my "uneasiness" around rooting for Paul certainly started to ramp up when Gurney showed up, as he was almost immediately dismissive and disrespectful to the Fremen. For some reason, I was surprised by that aggressive, somewhat arrogant behavior from Gurney, whereas Paul (and even Duncan in the 1st film) seemed much more humble and respectful in their initial interactions with the Fremen. Almost like Gurney didn't care to (or feel he had to) try to earn the respect of the Fremen. To be fair, we had not seen Gurney since the 1st film, we don't really know what earlier interactions he may have had with other Fremen when he was on the run. From his point of view - he too had to witness the death and destruction of the family, friends, house, life he loved and seeing that Paul was still alive obviously invigorated his lust for revenge.
There was a continuum of how the Atreides viewed the Fremen.
Paul was genuinely fascinated by them and genuinely wanted to learn their ways. Indeed, he becomes one in time, falls in love with a Fremen woman, and eventually becomes their leader.
Duncan is the next most interested: he's chosen to be Duke Atreides' liaison to Stilgar and genuinely respects them as warriors, though ultimately his interest is in forging an alliance with them.
Leto is next: wants to be respectful of them and their plight, wants to play the "the enemy of my enemy is my friend" card with them regarding the Harkonnen to form an alliance, though he's not much interested in their culture or getting to know them and their ways on a personal level like Paul and Duncan.
Jessica is next. The Fremen are purely instrumental to her. Play up the prophecy that Paul is the
lisan al gaib sent to deliver the Fremen to freedom. She becomes their Reverend Mother because she had no choice and she sees what such a position can do towards her political ambitions for Paul.
Gurney doesn't seem to like 'em.
There's a cut scene from Part One that goes like this. Everybody is having a little drinking party before Duncan goes to Arrakis to seek out the Fremen and well...
Gurney is the one who draws his blade to kill Stilgar when he "insults" the Duke by spitting on the table only to have Duncan stop him and disarm the whole situation by spitting back on it. I'm sure Gurney didn't come to like the Fremen more when he fell in with the smugglers, too, knowing that a Fremen guerilla band could attack the harvester at any time (and, indeed, that's exactly what happened to him).
He is also the most paranoid and has the deepest level of hatred for the Harkonnen...
...and thus is pushing Paul at all times to take revenge on the Harkonnen and the Emperor. He hunts Rabban down during the Battle of Arrakeen and begs Paul for the chance to kill the Na-Baron.
So, yeah, having Gurney back wasn't good for Paul's attempt to avoid his dark turn.
