Suppose everyone decides to say that "yep, that Islam sure is awful". What exactly is accomplished there? We aren't going to lock up everyone in the religion. So really how does pushing the angle that the religion is to blame in any way helpful?
What a lot of people don't get is we can't alienate moderate Muslims (who die in these kinds of attacks more than Westerners, it's just a blurb in the news when 50 Iraqi's die in a suicide attack). Islam is going through a rough reformation, and we have to make sure the moderates know they have our support. A ban on Muslims would be the biggest propaganda victory you could give to extremists like ISIS: SEE? We told you they hated us!!!
But it's hard to think geo-politically when people get blown up in Paris and massacred in San Bernadino. I live an hour from there. It's easy to get caught up in the "religion of evil" meme when these attacks happen.