First, what Lebron didn't wasn't in his best interest. He went from being Jordans potential successor to the NBA's favorite villan.
Secondly, doing "what is in your best interest" doesn't absolve you from the negative repercussions of your actions in any way.
Look if your boy says to you "radionstationrep, we are boys we grew up together, I will always have your back" and then one day he doesn't simply because "it wasn't in his best interest" at the time, that doesn't make it ok.
If Cleveland did something (the organization, team, coach, city, whatever) Lebron should have said so as a reason for leaving, in the same way if your boy goes back on his word he better have a reason for doing so other than "it was in his best interest"; or he is a selfish piece of shit.