There are checks and balances in place in the US to keep the Christian extremists in line, that will probably be slowly eroded away mind you. Drop them in lawless Yemen or Afghanistan and you'll probably see something similar...for example, the CAR which is probably the worst of the lot.
Like @limpid said, it's simply cultural bias to say one is significantly worse or better than the other when they're 99% the same. A whole host of geopolitical and other circumstances explain the difference in actions among the followers.