If you have ever been to a horse show and seen someone hit their horse because the horse wouldn't perform you'll understand. Learn and watch what your body is doing, get riding lessons, check for proper fit of tack, and check for injuries of physical problems of the horse. The same goes for your horse. I can't ever think of a good reason to hit a horse for the sake of punishment. I've seen many a farrier who will hit a horse with a tool if the horse won't stand still.
Many people believe that they get respect out of fear from their horse.
You know the type, they put the fear of god into the horse and they've got every training problem figured out. I can't throw a rock in my area without hitting at least one of these type of people. I've been on so many trail rides where you'll hear someone say that they're going to get a bigger bit to control their horse. This is one of the most severe forms of punishment that you can deal to your horse. You may have more control but it will be because of fear of the bit, not out of trust.