I enjoy watching boxing, but understand your point. However, the purpose of hitting someone in the face isn't to procure pain but to make the opponent lose consciousness (actually it's a lot more painful getting hit on a forearm). In a boxing match there's no hatred for the opponent, although some boxers need this to boost their performance, and no desire to injury or harm; it's just like fencing with hands in place of swords.

In many ways, boxing is one of the less violent sports around, both for those who practice and those who watch. I'm more of a football (soccer) fan than a boxing one, but if I had kids I'd rather bring them to a boxing match than to the stadium where they would grow learning that faking a foul can bring a penalty and the victory.