Well, I guess most here agree that potentially dangerous behavior in horses requires immediate action, and that can be a smack with a crop if needed... abuse is if done for the wrong reasons (like the horse doesn't do a maneuvre correctly), or excessively (like beating the horse through the whole corral, sorry, way too much and definitely just a panicky horse as a result that has forgotten what happened anyway).
Incitatus32, it sounds like you know what you're doing, and I'm sure if you come across enough horses, you do have some of the kind that you described.
My mare had troubles giving her hind hooves when I started working with her. She would pull them up too high and then make little kicking moves. I could have felt threatened I guess, since there was a chance she could hit me, and punish her for it. As it was, I thought that she might feel insecure with someone holding her legs, or that she might have balance problems or muscle stiffness. As she didn't aim at me doing it, I just told her no when she did it and practiced , making sure I stayed next to her with lots of room around us and not behind her when I lifted her legs. She learned she has nothing to fear, and now gives her hooves just fine.
By the way, I had only one real accident with horses (crazy, I know, I'm very lucky I guess, and I'm blessed with a fast reaction), and that was, funnily enough, when I was told to use a crop on a pony to make her gallop faster, which resulted in her turning into an unstoppable torpedo and me being knocked off by a lowhanging branch against the head (wore helmet, luckily).
Stan, it sounds like we have a similar way of handling horses, from what you write.
Faye, I guess we had different experiences with kids then. I don't know if lack of physical punishment and worse behavior are cause and effect or just coincidential correlations, since this is also the generation where kids eat more processed foods than ever, watch more TV, are under more pressure in school.... all these things and many more might make them behave worse (if indeed they do - even the old Greeks complained about how bad youth behaved those days). But that is, of course, completely off-topic...