The primary reason violent and/or insane Christians get all the screen time in computer games is simply that idealized, politically correct portrayals of Christians aren't interesting.
In addition, the way in which Christians wish to be portrayed does not jibe with reality, as evidenced by Desslock's implied presumption that the "tenets of Christianity" are uniformly benign, peaceful, and positive. They're purported to be (by Christians), but they are not, as anyone who's actually read the Bible or examined Catholic dogma ought to know—and even in modern times, the behavior and attitudes of Christian organizations and individuals reflect this. Vatican Palace is a gilded and frescoed, well, palace laden with priceless art, icons, and gold, and peopled by priests, cardinals, and bishops wearing fine fabrics (sometimes). It has its own bank supposedly worth billions. The Roman Catholic Church is the best and most obvious example of greed and corruption, but the leaders of offshoot Christian denominations very often live in luxury as well. A number of prominent and extremely well educated atheists have written or orated scathing condemnations of Christian organizations' tendencies to accumulate wealth from parishoners primarily for their own glorification. These documents or orations were much more eloquently executed than I could ever hope to accomplish, and also this is a computer game forum, so I'm not going to try.
Greed and corruption are only a small aspect of my distaste for religion (and not only my own), but they'll serve as an adequate example.
I was raised Catholic, and attended a private Christian school from kindergarten through ninth grade. I spent my childhood around priests, nuns, deacons, pastors, Catholics, and devout Baptists and Methodists. A great many of these people were and are, in fact, good (even wonderful!) people. My mother and sister are devout Catholics, and I love them both dearly. However, none of them are good people because of Christianity. They'd arguably be better off without it. They've been indoctrinated to feel that belief in scripture, God and Christ equates to being a good person. While they are still good people despite this, they are incredibly misguided, and religions on the whole are harmful to human society—used as a tool by the powerful to control and exploit the powerless, and by the powerless to delude themselves into believing there's a reward beyond worldly drudgery. Being based on ancient make-believe and therefore fundamentally ignorant, religion also very often comes into conflict with scientific progress and positive social change.
Violent and/or insane Christian cults may be "offensive to Christians", but are actually more realistic than an idealized benign portrayal of Christians. There have in fact been lots of Christian-flavored cults throughout modern Western history. Very interesting ones, too.
