Why does the government of the United States need a surface to air missile system at the Standing Rock protest camp?

Here is the story (or for those of you that believe that information from the The Daily Beast is “fake news” Here is the SAME AP story from Fox News).

Who, or what, the hell are they protecting here? This system is designed to take out cruise missiles, UAVs, fixed-wing aircraft and helicopters and the only groups in the vicinity that have this type of technology are the US and Canadian Governments and I don’t believe Canada is planning to attack us any time soon.

And if it is to protect an unfinished pipeline why is the National Guard charged with that task; something that you and I are paying for? Why not the pipeline company on its own dime?