I also agree with Corporal about striking towards people is a very aggressive behaviour. I can fathom that horses striking toward each other may be considered normal. But striking toward a person, is unacceptable (given this situation).
If my horse were to bite or act aggressive to someone and I didn't respond fast enough - I would have no issue of that person correcting my horse, so long as they used the 3 second rule. He would have deserved it.