There is a delicate balance in nature. Man is a part of nature, but a lot of leftist want to believe that we're not - that we're somehow an enemy. I don't believe this.
If we allow predators to take a role in harvesting animals, why can't we allow ourselves that same role. We ARE predators - that is just a simple fact. Can you imagine what our world would be like if we stepped back and said, "humans cannot affect the environment in ANY way." We must have an effect or we will just cease to exist. We might as well detonate all the nuclear bombs right now and get it over with.
I agree with hunting seasons, or paying people to control the herds. That way we still experience the joy of watching wild horse herds without the pain of having to see them suffer with starvation and illness.
Death is inevitable. Modern society doesn't want to accept this. We put people who are dying far away from us but, it doesn't change the fact. We will all die, hopefully without suffering.
That is the crux of this matter. Those of us who have horses and more importantly, find an inner peace with them, even the ornery ones, perceive suffering in the way the whole process of horse slaughter is done. The mustangs should be bolted upon the prairie that has been their home. A "Slaughter Truck" could be fabricated and the mustangs rendered meat on the hook in place. It simply takes the bureaucratic will and ingenuity.
As for domesticated horses, I am against their slaughter upon no other grounds than I consider it an offense to my soul to summon a horse that has borne my weight and compel it by its tameness, to suffer un-humane transportation to a slaughter house. The only reason, IMHO, for a tame horse to be put down is illness and suffering. To send a horse that has worked or played with you to slaughter is somehow, immoral to me.
Let me add that this "sentimentality" is not limited to horses, nor do I believe confers upon my character a "weakness". To the contrary, just the opposite. It has been my experience from battlefield to the hay field that the lack of empathy was a good indication of a lack of courage.
One last point, the American shipping millionaire, Henry Bergh, started the ASPCA in New York in 1866 because of the mistreatment of horses. He also went on to found the SPCC in 1874. That was the Society to Prevent Cruelty to Children.
Those who are cruel to their animals are cruel to their children, and vice versa. Harvesting, culling herds, being predators ourselves, are all peripheral to the point of actual contention which is cruelty and forced suffering. To the animal and to ones own character. We all, man an animal alike, would like to pass through this life with as much unnecessary suffering as possible.