Christian goes mad with a gun - mental problems, work problems etc
Muslim goes mad with a gun - terrorism.
It depends on what is discovered to be the motivation. If a Christian goes mad with a gun and says he did for Jesus or God, I guess the fact he's Christain becomes relevant. Most Islamist butchers scream Alahu Akbar, leaving us in no doubt they believe they are doing their stuff in the name of Islam. When Muslims go on the rampage, this is commonly the case, so people make assumptions. To be expected really.
But then just because a Muslim shouts Allah Akbar, doesn't mean that the main reason is because they're a fundamentalist Muslim.
If a Christian American gets pissed at the US govt and wants to take revenge, what will they do? They'll probably go shoot some people up, they won't shout religious slogans. They going against the US govt.
If a Muslim American gets pissed at the US govt and wants to take revenge, what will they do? Seeing as Bush kind of declared war against Muslims, showing why they're angry at the US, for the war in Iraq, the vilifying of Muslims, for all of that, you're going to declare you're a Muslim and make some kind of religious noise.
But what's the difference? Perhaps they why they got angry is different, a Christian is probably less likely to get angry over foreign policy, and more over internal policy, but still, it's anger at the govt.
If a Christian shoots up an abortion clinic and doesn't make religious noises, does that mean religion wasn't an issue? Doubtful, religion is an issue, however it's a simple case of Christians just not doing that, not shouting God is Great when they go kill people for their religious beliefs.