Should people who beleive in Islam be allowed to live in America?

I just watched a doentary on TV about the Karachi kids who were abducted and sent to Pakistan to be brainwashed into hating the USA, so they're now potentially future terrorists. They're now back in Atlanta with their parents ... who knows what their parents are planning. I did some research and apparently Atlanta has a huge Muslim population and one of the largest Mosques in the United States. Is this a threat to our nation?