You have a very simple version of everyone else and more complex version of yourself. We're all fucked up and complex. Give other people that credit.
Islamism isn't a racial demographic. It's an ideology. It can spread by the changing of a mind.
At their core most people vote based on group identity, emotional activation, and subconscious cues. You seem to have a far too idealistic view of human democratic behavior.
I wouldn't say that process is a simple one, it seems to be pretty complex(at least biologically), but I would say that more often then we should, we mis-interpret and confuse confirmation bias with a process of rational critical thinking. Or seek to explain highly irrational processes with too much deference to rationality.
And to bridge that with fears of radical Islamic conversion, there is so little influential power of that ideology in this country - a country that is trending toward agnosticism more then anything - that the level of focus on that particular issue defies reason. Which falls in line with what I just said.