for me this would be a reason to leave bitcoin completely.
the major exchange doing stuff I don't like would not be a reason for me to abandon bitcoin at all. It might be a reason to abandon that exchange. I wouldn't even abandon bitcoin if there where no exchanges left.
Me neither, at least not yet. Let's see if the incentive structures of bitcoin work out. I doubt this miner is acting in ignorance to the fact that he might be hurting himself badly when mining well >50%. After all, pulling this off took quite a few resources (whatever these are).
Criminal or not: Big fish ain't stupid.