Simple answer? Pure Fear. How intelligent are those who invite known criminals into their home then expect to Not live in fear? Sure all Muslims are not radical terrorists but the Only difference between a muslim and a radical muslim is how devoutly they decide to follow their religion. Pretty simple. Most prefer peace but it only takes one to go off the deep end.
The difference between a radical Muslim and A moderate Muslim is that the radical Muslim wants to behead you and the moderate Muslim wants to watch.