Is any law enforcement guaranteed to be exactly correct? No, because every person is fallible, and every system is made up of fallible people. This is why we separate arrest (police) from trial (judge) and judgment (jury), to mitigate those risks.
To malign a system because it is imperfect is to be unrealistic. Surely, we should minimize those harms, but they are not a reason to abdicate our laws.
These things are not being separated though. Your agents are executing citizens in the street. This is not about illegal immigration at all. It's just straight up oppression.
To malign a system because it is imperfect is to be unrealistic. Surely, we should minimize those harms, but they are not a reason to abdicate our laws.