Never say never. And we have done it before. Making the now optional employee verification system mandatory and eliminating all non-emergency benefits to Illegals would send many home on their own. Any trouble makers that engage in civil unrest will certainly firm up our resolve to deport the stragglers.
I'm certainly in favor of making illegals' lives more difficult- if you enforce current laws and make it tough for them to get a job, collect benefits, receive health care, go to school etc., you'll increase the natural attrition rate of illegals going back to their home countries.
But a round-up like we had in WWII of Japanese-Americans? I can't see Americans having the stomach for that, and rightfully so.