I'm still thinking about Star Wars (which also happens often enough), specifically about The Last Jedi, which has proven to be a source of contention among some of the SW fan base. It had some high highs and some puzzling lows, but I liked it well enough anyway. One of my quibbles was the seemingly pointless detour into Canto Bight, the casino city. But reflecting back on it, through the lens of the Kirk-Spock-McCoy triumvirate, I now see that it wasn't a complete waste of time at all, even if it dragged on too long and came dangerously close to some of the more terrible, cartoonish elements of the prequels.
The key lies in the line Finn utters when he finally defeats (or has he...?) Phasma, proudly declaring he's now "Rebel scum". Let's get this out of the way now: that's a terrible one-liner; it makes little sense for Finn to say that in context. (Maybe "Resistance scum" would be a shred better?) The line is purely there as a callback to Return of the Jedi, meant for the audience and not the characters. Words for fans to recognize.
Putting that catchphrase aside for the moment, the casino detour is the culmination Finn's character arc, stretching back to when we first met him in The Force Awakens. In that one, "Big Deal" Finn was out for himself, lying about being in the Resistance in order to save himself. Later on, he agrees to go to Starkiller Base, to help disable that battle station, sure, but mostly to rescue his new friend Rey, not for really for the greater good of the Resistance and the Republic.
In The Last Jedi, upon realizing that the Resistance is in dire straits, Finn takes off again in hopes of finding Rey and preventing her from returning to the fleet and near-certain death. Not really the "Resistance hero" Rose thinks he is. To help out his buddy Poe, Finn goes along with a plan to recruit a hacker to disable the tracking device that the First Order is using to find the Resistance fleet.
From the very first, Finn is out for himself and his friends, not a greater purpose. But, beginning with the adventure on Canto Bight, we get a turning point for his character.
There are a couple minor points brought up on Canto Bight (which could turn out major future SW works, we'll have to wait and see): the ideas that Force-sensitive people can be anywhere, and that the true villains are the upper crust profiting off war and misery. Where better to make that latter point than a decadent casino, far from the consequences of the struggle?
I fully acknowledge that this particular B-plot could have been shorter and more subtle, but I realize now it definitely had a purpose: to turn Finn from an incidental hero into someone who is ready to sacrifice himself by flying into a superweapon, something he would have accomplished if not for the emotional Rose coming to the rescue. I expect Finn to be in full-on hero mode in this trilogy's final chapter.
But I still don't get why he says "Rebel scum" though.