"but it's no deterent to the others, and would cost a bundle. "
It's a deterrent. If they had all their posessions seized (yes, the Consitution only protects citizens, not illegals)and were booted back to Mejico with only the clothes on their backs, that would deter them from coming back and others from coming.
Plus, they wouldnt have any more money to pay another coyote...
"It's a deterrent. If they had all their posessions seized ..."
Obviously, what they had with them would be subject to "abandonment" rather then them being held in jail for trial.