I mean dude played 11 seasons for the same team. In the modern NBA, that's pretty loyal. At this point in his career, he's entitled to go try and chase a title with a contender while Portland tries to rebuild. Same thing Clyde did. Same thing Barkley and a hundred others have done. I'm not a big Dame fan (even at his peak, he was never a top 5 player to me) but this is the kind of situation that the free agency era is built for: star players not being stuck on perennial losers their whole career and teams giving themselves the flexibility to rebuild with draft picks and young prospects.
It's certainly gotten out of hand post-Decision (while it was always LeBron's right to go out and find the best deal and situation for himself, I'll always hold that against him in any conversation about greatness) but players don't owe anything to franchises and cities beyond showing up and playing ball and, in a lot of cases, fans should aim their anger at poorly run franchises rather than players who skip town because they recognize a loser when they see one.