I find it slightly easy to be the dick in games.
I mean, my first game where I got to be an utter and total dick was any game from the Ultima Series. I COULD HAVE gone through the main story line, but no, I decided to steal people's shit and kill everyone for their goods. In Fallout, when I get fucking mad, I just save the game and commit a total town massacre, then restart knowing that I need some of the people.
I also tip Brahmin because it's fun, though I try not to kill a lot of the animals, unless I need food.
I feel no remorse for what happens in the video game world. That's why it's so easy for me to kill everyone in the strip club and hang out there with a rocket launcher, just blasting everyone that comes in. Or to go to where the hobos hang out and just run them over with my truck.
In Fable, I tend to be a dick too.. cheat on my wife with dudes.. cheat on the dudes with a new wife... do a couple of quests so they like me again and then start all over.
Plus the sword you get from killing your foster sister in the end is too good to pass up.
In conclusion, it's the player's choice to be a dick or a saint.. or even neutral, it's just more fun to some people to be the dick.