The argument used to be
that these (gestures vaguely at videogames) are games being made by predominantly men, being played by predominantly men. It's easier for both designers and players to relate to what they know, and in an industry that strives for empathy (Or should do, at the very least) picking white male protagonists is a numbers game. It's supposedly easier for men to empathise with men. As Dara O'Brien once said in his standup about why he doesn't do Islamic jokes:
[People used to come up to me after gigs and go] You'll make jokes about the Catholics, and the Protestants, but you wont make jokes about the Muslims, will you? To which I would say, there are two reasons I don't do jokes about Muslims:
I don't know a fuckin' thing about Muslims.
Neither do you.
That's not to say that people shouldn't be making attempts to bridge that gap, and it's disappointing that the easiest route is the route most travelled. Just because I have a penis doesn't mean I can't relate to someone without a penis, and there should be more effort made to make both male and female characters that actively attempt to relate to a wider range of players. However, when you consider that most games contain fairly minimal character development, the role of protagonist becomes somewhat redundant, and the argument is one of principle - that a certain type of person is being under-represented by the medium as a whole. I get that; the standard white male lead doesn't fairly reflect a culturally diverse society, nor his position of dominance over the other characters and the world he inhabits. This flag is being waved by some people who won't even play the game, and it's a larger issue that videogames can't take sole credit for.
Looking beyond these principles is the core issue:
Personally, unless you're going to actually explore the unique perspective that a different faith/gender/race could have on the game, it doesn't fucking matter what your virtual murderer looks like.
It's a shame that more people, both developers and players, don't agree with (or are even aware of) this, and that steps are not being taken to do something about it.