If an actor acts the same way as he or she does in real life, I feel they are not doing their jobs correctly. When they play a character on screen, they should try to fulfill the life of the person being portrayed, and should in no way reflect the way the actor lives in their real life.
This is the stupidest question about acting ever.... Why the hell would somebody need to be the same in real life as they are while acting? What is the purpose of ACTING then?! there are many actors and actresses who apparently are very pleasant in real life while they can play the part of a person you just want to kill with your bare hands.
Should an actor be forced to play roles only depicting his or her real life persona? Should an actor be limited to playing only the good guy or only the bad guy because that is his or her way of life?
I believe that an actor or actress should be able to choose what kid of acting he or she wants to depict. Just because someone is a great person in real life does not mean they are unfit to play the part of a bad guy. Take for example Alan Rickman, He palyed the role of Hans in Diehard. Im sure the real Alan Rickman would not take over a building to steal money. He wouldn't hold several people hostage while his people broke into the vault. Alan Rickman is a great actor able to step into the role of villian despite his off screen persona.
If it were a requirement that an actor's on screen persona match their off screen persona, they wouldn't really be acting so much. They would just allow themselves to be recorded in a specific role. A good actor is able to inhabit different personae in order to convey the appropriate personality for a given movie or television show. It shouldn't matter what they are like off screen, just as it shouldn't matter what an athlete does off the field.