I can't tell if the problems is, people just do not believe generalizations can ever be made, or if people are so afraid of racism that they're willing to die (or at least let their neighbor die) to protect the rights of those who, while they fit the stereotype, they are not evil.
Inevitably someone steps up and says, "Muslims are killing people all over the world" and the response is to point back hundreds of years to when Christians were guilty of the same.
Someone says that, "Terrorists are Muslim" and someone points to one or two non Muslim terror attacks in the past few decades.
In my job I cannot rule anyone out as a Terrorist. Ever. At the same time, I can't say everyone is a possible Terrorist.
Let me put it another way around. We have something called BOLO's that get posted every now and again. It means "Be On The Lookout". It has nothing to do with Terrorists, although a Terrorist can be a BOLO. But a BOLO can be anything or anyone. Maybe a bank was just robbed and so they put out a BOLO on the suspect. Or maybe there is an Amber Alert and so they put out a BOLO for the child or the kidnapper.
You get the idea.
Now, if I get one or two BOLO's a week, that's not a problem. That's how the human mind works. I can focus on looking for one or two different people that cross my path. I can take a double take of someone each time the description hits me. For example, if i'm looking for a tall, blond, blue eyed, male in his mid 50's, with long hair, then every time I see someone with that description, I can look again to see if they fit the picture.
But when you start putting 20, or 50, or 100 BOLO's out every week, forget it. There's no way I can look for that many people. It's just not possible, unless you've got a photographic memory.
So, I can assume every single person is a terrorist until they satisfy me that they are otherwise (Which is like getting 1000's of BOLO's every week) or I can narrow down my realm of possibilities and have a much better chance of stopping a terrorist.
I hope that made sense. My point is, if you make me look at everyone equally, then no one will ever be stopped. If you allow me to combine my experience with my knowledge and past encounters to do my job, i'll have a much better chance of keeping all of us safe.