Do Border Patrol agents carry guns because they neatly accessorize the uniforms, or what? Why are they not allowed to use their weapons when under attack?

I keep reading that the mexican drug smuggler involved in the beating of Ramos and Compean border patrol agents intends to sue the Border Patrol. How is this possible? I thought the US government could not be sued...? Also, if that is the case, can the US government counter-sue the Mexican government for the millions of illegal aliens living in our country?

Sometimes when the border patrol stops illegals from coming into the USA, their buddies throw rocks at the border patrol. The border patrol shows great restraint and do not use force against these people, who could potentially cause bodily harm to the officers.

A vehicle which had crossed into the US illegally struck and killed a border patrol agent. The Mexican government has not done anything to stop the flow of illegals and has in fact aided people trying to come into the US. They should be held liable for this man's death. If our agents are going to be sued for doing their jobs, then the Mexican government needs to be held accountable as well.