Middle-Eastern male, beard, within the age most likely to be radicalized.
Questionable parentage - where's the paperwork? What's he trying to hide?
Some questionable associates - criminals, the poor, etc.
Clearly has some history with violence - which means he's likely to commit same here, right?
Radical ideas that clearly don't fit with the mainstream.
Clearly has an agenda - ie, he's not here for us.
Dear Immigration officials - if you see a dude like this trying to get into the country, turn him back.
We don't need his kind upsetting our perfect little applecart, do we?