It makes sense that  Sharon O'Toole, a rancher would write such a biased article about America's wild horses.  As others have indicated, equines are no exotic species, they are a re-introduced species having evolved on the North American Continent 3 to 4 million years ago. Yes there were several extinctions with the last about 10K years ago from overhunting by native peoples. However, these animals belong here and are part of the native Fauna of America. They graze only the tops of grasses allowing for new growth, whereas the  true exotic species, namely cattle, tear up the entire grass, leaving bear ground. Horses are migratory in that they graze, move on, allowing the area to regenerate.
Please do not be fooled by this very biased article. Do your own research.( read awionline.org,' Wild Horses as Native American Wildlife', only one reference of many)  Much of the negative information about wild horses is dispersed by the Cattle industry,their lobbyists and misinformed media.