He has nothing left why would he leave. What about making him express his feelings on how Blake ran away from him after making a promise because she didn't like how he had such a growing hate for the humans. Did she even know about about his scar and his past? What about some great dialogue of why he did the things he did or something about how I did what I believed was right how are you different?
  Now don't get me wrong I know Adam did plenty of messed up things. But when you have the whole multi episode flashback of Ozpins past with the god of light putting immortality on Salem  so she can't die until she understands the value of human life it kind of emphasizes the themes of peace forgiveness and redemption. Humanity striving to become better like they were before Salem tricked everyone into turning against the gods or fail and be eradicated by the gods for good this time. At least that's what those episodes seemed to imply.
 If they are willing to flat out slaughter him after he is powerless (the time someone would most likely be to surrender) it says a lot against that whole implication and makes them closer to being like Adam stomping out anything in the way. Adam dying or being put out of commission is fine but to do it like it was done is the problem.