StarCruiser, That's not a very fair argument (and the part about them having "evolved here first" is hardly agreed-upon in science). Yes, horses evolved here, and yes, there are skeletal remains of the "modern" horse in North America. But those all died out around 12,000 years ago.
Only the re-introduced modern horse has descendants in this continent.
I think it's reasonable to say that a species that has been absent from any region for more than 10,000 years is no longer a "native."
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To be honest, the whole native/not native argument seems to be disingenuous shenanigans on both sides of the argument (in other words, they're trying to use some "natural" argument to bolster their position). Let's just be honest about it: They are no longer a native species to this continent, but they have clearly become integrated into the environment/ecology of our nation. Therefore, as a matter of responsible husbandry, it is our duty to manage the herds and keep them in balance with with other species who share the range with them. Sometimes this will mean assisting them by providing water in droughts, and other times it may include culling herds to remove disease and protect diminished food supplies.
My personal opinion is that they are beautiful, majestic creatures and having some herds roaming free is both good and noble. I firmly reject any twisted notion that the primary goal of environmental policy should be to return our wilderness to the state of some mythical pre-human paradise. Our goal should be to create a balance between preservation human need.