Obviously, the ICE agents have to rationalise what they do. "We are the good guy, we work against the bad guys". But I don't think that they wake up in the morning hoping that they will have an opportunity to hurt what they themselves consider "average americans".
Looking at the video, I could totally imagine that the first shot fired was a mistake, and then one or more of the agents panic and shoot... well... a LOT of times. That doesn't seem rational, or professional. I don't think that the agent thinks "ahah! Here is my opportunity, I'll shoot him 5 more times". Still, they killed someone for no apparent reason (it's not a proportional defense, quite obviously) and they should be judged for that.
Yes, please don't give those people guns.
Then why are they letting people take these positions without specific training and why are they letting them return to work immediately after making fatal mistakes? Why are those above them immediately covering up their mistakes and why are their colleagues illegally tampering with evidence after the events take place?