But not being "devout" -- even judged by some theoretically objective standard if there were such a thing - isn't, by any means, the same as being atheist or agnostic...
The journey to being free of religion begins by not caring as much about religion. I'll give you a data point for why I'm saying this.
Mass Attendance Down 2/3 Since Last Papal Visit...
Western people and western values distinguish themselves by having developed in a Christian / Catholic environment that grew to tolerate, that began to harbor, and eventually was overcome by ideals of freedom and democracy.
From the Dark Ages of religious wars, our people have become quite secular and will continue to trend that way until organized religion no longer means anything. Our civilization makes steady progress.
A person of devout faith should be seen as a threat to that progress, depending on who they are and how fervent they are with supplanting western law with their own form of crazy. Muslims, whether they are foreign arrivals or freshly converted, are viewed as more devout and more insistent on a form of religious law that is simply not compatible with the historical values of western civilization.
Their devotion is seen as a change backwards towards something that is not historically western. Not historically free or democratic. Modern political leaders in the west have no such religious devotion, and I see Carson's comment as the logical continuation of our status quo. I stand by such personal qualifications for our elected officials. If you are what you claim, then you should too.