The name"Guardians" implies their purpose was at some point to protect... Something... The question is, what we're they protecting, who were they protecting it for/from, and why now do they roam the earth blasting **** with lasers? That doesn't seem much like guarding, more like eliminating. I think their original purpose was corrupted, whether that was by Ganon's power or otherwise has yet to be determined. Perhaps he found out how to control them, or perhaps they broke free of their original masters' control for whatever reason. Did anyone confirm that they were built by the Shiekah or is that just speculation? I don't remember, and I think a separate force creating them, perhaps against the Shiekah, could lead to interesting developments.