You start shooting at the border and political sentiment will turn on behalf of illegal aliens. Therefore, it's not just an immoral idea, it's stupid as well.
There is a lot of shooting going on at the border now --- often the drug cartels carry out an execution on the American side of one of their own. No big deal. Border patrol agents have been shot and murdered --- again -- no big deal. You've got hundreds of illegals dying out there in the desert -- lately many from their coyotes giving them stimulant drugs like cocaine to make the trip over easier but those drugs didn't mix well with over 100 degree heat --- and many of these are pregnant women heading over for their life of welfare checks but just didn't make it. You've got the Mexican police murdering opposing cartel members and about 400 murdered girls and women in just one border town. No one really cares --- I don't think what you say would create some big ripple either.