It is racism, the false idea of "a lot of them" just shows how blind ignorant a person might be.
I'm yet to see the first Mexican in US soil to execute a terrorist attack, immigration control is not a solution, and forcing a complete ideology is just a form on modern Nazism. The west proudly sells an idea of freedom which is the whole point of why people go to such places, hence why people got out of their places they belong in the first place, the idea of them culturally colonizing them is an stupid idea indeed, if they go to such places is to find a better live than what they have or adopt other culture different to them, not to impose their culture into them, because that's what the west does.
The lack of cultural exchange and recognition is the worst form of racism, people being paranoid of "them" makes them blindly ignorant, I have had the luck of experiencing different people, cultures and ideologies. And thanks to that exchange I get to see the world in a wider spectrum, I know Muslims, Jewish, Buddhists, capitalists, extreme communists, socialists, etc... I don't affiliate with any of them (me personally be an atheist, and a bit of a left wing guy), yet I am not influenced by them, I understand their goals, needs and struggles and all I see is different people, not their ideologies, avoiding such an exchange and diversity is what makes the world stupid and retarded and is what fuels the worst parts of retardation and the worst atrocities witnessed in human history.
Yet, people won't learn, they want the safe heaven for themselves, blindly living in that bubble of ignorance.
At the end of the day is a struggle between "X" and "Y" powers, while the population is being told lies and manipulative information just to increase that cultural divide, which is what makes everything worse nowadays and why the extremists exists in the first place.