I've got a theory about the "wetback" joke. I think you guys may be approaching it too literally. The joke isn't about how Mexicans are easier to kill than other nationalities. Rather, it's about how Mexicans have so little value that the only worthwhile thing about them is that they can be killed, and the "joke" is that mortality isn't unique to Mexicans. A clearer wording might have been: "What's the only good thing about wetbacks? They're mortal and you can kill them with bullets."
Thank you for your time and consideration.
