The hate may be bit exaggerated, but not necessarily unjustified.
He turned him self into a "bad" guy, don't forget that. You either like him or hate him..
I personally don't care either way, but I do wish him speedy recovery.
Brock was getting booed before he ever set foot in the Octagon. Fighters that he has gone on to destroy (Mir/Herring) have completely dissed his pas career and show zero respect for him.