Arenas is not as bad as you say. He's made some stupid decisions, but as a basketball player you can't say he's not talented. Him and Jameer Nelson is redundant, but Gilbert brings more play-making ability because he's just more talented and bigger. He's also had to go through a Michael Vick type transformation and we all know how thats turning out.
So because Michael Vick was able to re-closet his demons, it means Arenas and all other players are a lock to do the same? There is no guarantee that Arenas doesn't plague the Magic just like he did in Washington.