Almost everyone here is right at the same time. It's his call, it abides by the rules, it's taking the easy road, it's great for NBA publicity, it harms parity and uncertainty in the league, etc.
I think Durant's worried about his legacy and not wanting to be one of those guys that got their stats but never a ring (Malone, etc), and probably issues playing with Westbrook.
Really, the NBA should have done more to maintain a level playing field. Now, a team can instantly go from dark horse or contender to rebuilding with one move.
One option I like is the idea of a hard cap, but no maximum player salary. So, LeBron can get paid $50-80m, but might not have the best team around him.