Actually, you shouldn't beat children because they /can/ fight back. If you re-instated corporal punishment, schools in bad areas would be ridiculous almost immediately, and as soon as you get an out-of-control adult or a victimized-feeling student, someone is going to get a gun from their older cousin.
Besides, when was the last time you were in a high school? The teachers are mostly older women, who most definitely cannot afford to play a game of physical escalation with teenage boys.
Actually I'd be curious to see what would happen if corporal punishment was re-instated. I think your scenario derives from a hyperbolic world presented to us by a hype-machine media. I'm not sure it's really accurate. My hypothesis would be that it would in fact cut down on problems, though I won't deny that one or a few incidents like what you posit could happen. Truly "rotten apples", few in number as they may be, are in every part of the population. This is also why re-instating corporal punishment would be extra-hard -- there will be "rotten apples" doling it out, too.
Also, to address your second point, when I was in elementary school and a few kids did receive corporal punishment, it was always meted out by a principal, and not directly by the teacher.
I went to a public high school less than ten miles away from Richmond High (http://articles.cnn.com/2009-10-27/justice/california.gang.r...), I may have a slightly skewed perspective. But on the other hand, I don't think corporal punishment would ever be an issue in richer school districts.
The part that scares me the most isn't the students though, it's the `adults'. The amount of evil and incompetence from the school board level down is astonishing. I wouldn't trust those people to take my order at a fast food restaurant.
Besides, when was the last time you were in a high school? The teachers are mostly older women, who most definitely cannot afford to play a game of physical escalation with teenage boys.