How about we do this, start checking EVERYONE, and if they're here "illegally" whether they overstayed their visa, or committed the crime of entering illegally, they get chipped or branded somehow, and returned to their OWN country, and never allowed to set foot in this country again. 
As to those who hire illegals?  Massive fines and or seizure of their businesses.  
Illegals of any stripe, should be kept from education, medical, and any other "benefits" of American citizenship.  Not allowed to own or rent homes, vehicles, businesses, etc.  Many would have to self-deport.  That would also impact the crime levels as they have to commit crimes to stay!  
And I'm assuming the last sentence in the letter was rhetorical.  Unless it was really a threat, if so..you're on the losing side...I mean, if push comes to shove.