Earlier quoted context omitted.
The brain tumor was removed...and the public behavior was unchanged. http://valleywag.gawker.com/rap-genius-frontman-blames-brain...
Sad but the brain tumour could still be the reason for his behaviour. We don't know nearly enough about the brain to argue that the removal must restore the previous personality.
It's the same reason that we shouldn't let blind people fly commercial airliners. Flying requires vision. Running a company requires good judgement.