I would like to make the distinction between “survival” and “comfort.” Sure, a dog will survive chained to a doghouse in subzero temperatures, but we all know he is going to be miserable. Same with horses. They can survive weather extremes, but are they comfortable doing so? Many are, many are not.
I pride myself on developing a working relationship with my horses, and part of that is seeing to their individual needs. Isn’t that how man and horse bonded in the first place, with us providing food, safety, and protection from predators, and in exchange they allow us to climb on their backs, stick needles into them, get into claustrophobic metal boxes and jostle down the road, jump fences, dance in place, etc. etc.?
To that end, I enjoy providing my horses with what they need to be comfortable. As I posted earlier, most of my horses have never needed to be blanketed, but now I have a TB who does. Would he survive without one? Of course, but then I’d be buying another round of ulcer meds in short order.
To each his own when it comes to horse management. I just object to people issuing definitive statements like “Horses don’t need blankets.” Perhaps that’s literally true, but some horses really do need them to live a comfortable, happy life.