Unlike your local police department, which has necessary law enforcement included as part of its mission, there is no legitimate law enforcement function for the United States Border Patrol. If you don't like undocumented Mexicans, you don't have to hire them. If they stroll from Nogales, Sonora into Nogales, Arizona with backpacks full of recreational drugs that you and your family don't like, you and your family don't have to buy any. The people aren't violating anybody's rights by bringing themselves and their property into the United States, and the government does not own the United States. It's boring for the first 9 frames, so you can skip that and start here if you prefer.
People have a pretty good reason to be furious about such conduct from the police.
You see, there is an actual need for some laws, and a need for the enforcement of those laws, but there is no need for the Border Patrol. The United States has been described as a nation of immigrants. So, in all fairness to the police officers, average police don't deserve to get killed nearly as much as Border Patrol goons do. Some police officers sign up so they can serve the people, accepting the job of enforcing the many unjust laws as a required trade-off. That is a decision they have made and, while it is the wrong decision, at least they aren't as bad as Border Patrol goons, which sign up only out of greed and malice.