Yeah,you listen to the horror stories of the people who live near the border,especially in Arizona.If one of them were to begin picking off these law-breakers for trespassing,you can be sure that we'd see arrests at the border.Arrests of American citizens trying to protect their property and families.
Reminds me of the story of the guy who heard burglars in his garage,called the police,and was told that no one could be there for a half hour.The guy calls back 2 minutes later,and says,"Don't bother,I just shot them".In two minutes the place is crawling with police,who arrest the burglars."I thought you said that you had shot them",says one cop."I thought you said there was no one around for a half hour",the guy replied.Of course,in our world,they would probably arrest him for filing a false police report.
That'll teach us.