Because we Americans won't be marched into railcars and sent to camps when our government decides it doesn't like us.
If history is our guide, most would ship off without resistance. Soldiers and and police would be glad to strip them from their homes and families, in the name of Homeland Security.
The few holdouts who defended themselves would be remembered as traitors or terrorists, or not remembered at all.
1942: PASADENA, CA -- American soldiers supervise the rounding up of American citizens of Japanese descent, as they board trains to be shipped off to internment camps. This train was heading to a camp in the Mojave desert.