I agree that no one should ever be raising their hand and hitting an animal in anger, except perhaps in self defence, as a last resort, if a bear or a dog, for example, was intent on attack.
In ordinary equine training situations though, there is absolutely NO excuse for anyone to be hitting a horse with intention to harm. As many horse people below have stated, if you have to resort to that, then you are simply demonstrating your lack of skills.
However, I disagree that this thread ought to be shut down because somewhere along the line, the subject of spurs and crops and their use was introduced, which is a totally different topic really, and I think equestrians and those with daily hands on experience of horses, should be allowed to put their different viewpoints across.
I own a horse that is all muscle and weighs 850 kilos, whom I love like one of my children, and if it were necessary, I would far rather give him a light guiding tap on the shoulder to reinforce an aid, than yank the reins or, God forbid, his mouth.
Most of the time it’s not necessary, but I have been in a situation when I was riding a short distance in light local traffic to get to a bridle path, and my horse was spooked by a loud motorcycle, and he turned his hocks slightly towards the cars, jogging along slightly diagonally, and it was very helpful to be able to use my crop as an extension of my arm, to hold the line as it were, to keep him, me and other road users safe. But a crop should always be used positively to guide or reinforce an instruction and never to punish.
Equally, I don’t use spurs because I don’t compete, but would far rather a skilled rider with a good seat used a very light touch of a rounded blunt spur on my horse than have someone kick his flanks to get him to speed up. Again, it is necessary sometimes to get your horse to move forward promptly in order to be safe.
Neither the tap of the crop or the slight precise pressure of a spur are intended to harm, but to guide, steer, reinforce and encourage, which is perfectly acceptable imho if done calmly, intentionally and correctly.