Alright, I'll note the most important caveat: it is not Islam but Islamists and Islamism that are at fault in this ongoing outrage. But still! Wouldn't you think there'd be a protest or two somewhere in the arc of Muslim faith that stretches from Indonesia to Morocco and southwards to the deepest reaches of Africa? OK, maybe it takes courage in those lands to stand up and say, "No, this is not the Islam I was taught and in which I believe."
...it is just factually wrong to say there is no evidence of revulsion in the Islamic world. Why does it matter? Because it's too easy to adhere to this narrative--all of Islam's the problem, somehow--in place of asking the serious questions that need to be asked about this bombing.
...some group clearly is trying to start a sectarian war, and may well succeed--an unimaginable catastrophe for Egypt and for the region. It's pretty damned important to know which group. It matters a lot whether this was the work of al Qaeda or the Egyptian Muslim Brotherhood. The implications would be very different. The answer "Don't get bogged down in the details, all Muslims are the problem--they're either doing this or they support it somehow" is not remotely useful to formulating any kind of policy response (and also not true).