In almost every psychological study I have read, playing ("just") a violent video game resulted, on average, in a more violent, aggressive attitude in real life. All the gamers who, for whatever emotional and personal reason, claim that that isn't true are simply ignoring experiments and data.
(Note that causality is
not established -- e.g. do violent video games actually make people violent, or do they only offer an avenue of violent expression for already violent people, which expression remains [at least temporarily] heightened after playing? Moreover, it remains to be seen whether a cathartic effect exists. Also, there is no value judgment in this correlation -- it is the assumption that violence is not good that puts a negative spin on the issue.)
Also, brain scans show that observing someone perform an action triggers the same areas of the brain to fire as if the observer had performed that action, and is believed to be important in learning. Whether this is pertinent to film and video games I haven't read about.
As far as being a bad person because of doing something in a virtual world that would be bad in real life (let's restrict our definition of "bad" to the player's definition) -- an interesting question. On the one hand, I remember the first time I played GTA 3 I thought it was awesome that I could kill anyone and steal any car -- but later came to the feeling that I didn't like being a bad guy. I felt that somehow it was wrong of me to do bad things, whether in life or in my mind to non-living artificially intelligent electro-visual constructs of code.
On the other hand, I can't believe that it is necessarily wrong for an author to create a bad character in detail, and many of you on the forums play TES the way an author plays with characters. I myself like to think of my character's story in a detached way sometimes. (Usually, though, it's
my eyes I'm seeing through into the TES world.)
Those were my long, though truncated thoughts. Short answer: It is an important question, because the answer is not universally and thoroughly
no, but the answer is also obviously not always
yes.