I have encountered quite a few Christians who seem to have difficulty understanding why growing numbers of atheists are speaking out. I often explain that we speak out because we are invested in our surroundings. We do not share their belief in an afterlife, so we do not have the luxury of passivity. I point out that we often speak out because we feel that we must. We feel this way largely because they continue to push their beliefs on us through a combination of evangelical and legislative efforts (e.g., opposing reproductive rights for women and same-sex marriage while demonizing us for rejecting superstition). In the face of such efforts, tolerance is not viable.
I can imagine a sort of Christianity so divorced from politics and so uninterested in gaining secular power that most atheists would probably ignore it. It would be so irrelevant to us that criticizing it would be pointless. But this is not the sort of Christianity we have in the U.S. today. Not even close.
Instead, we have a form of religious belief that is not merely irrational but harmful. In such a context, wouldn't we have to be crazy not to speak out? Even if the harm wasn't so frequently directed at us, wouldn't we still have some obligation to address it?