Certainly there are people who are cruel to animals of all sorts - horses, dogs, other humans. I don't like going to work every day, but if I stayed home without any purpose, I'd get bored, start feeling useless, and eat cookies until I was 300 pounds. If I lived in a hunter-gatherer society, where most of my day was dedicated to my physical survival, different story.
If my horse hated being ridden, I don't believe he would come to me when I called his name, walk willingly from the pasture to the barn, willingly accept his tack, and happily ride me about. He is much bigger and stronger than I am. I like to think I am marginally smarter than he is, but if he didn't want to be caught, he wouldn't be. If he didn't want to be in the cross ties and be tacked up, he wouldn't be. If he didn't want to be ridden, he certainly has the ability to buck me off and head for a life of freedom
I believe it is a good thing to contemplate our relationships with other creatures, though. It's important to sometimes step back and consider if we are being good stewards of life's treasures, including horses.