The thing that bothers me most about this is that the kid's parent(s) obviously sent him out and/or approved of his actions. I'd feel the same way about this if the kid was tearing down an Obama sign - you just don't go messing with other people's stuff. And, it doesn't make it "ok" because you disagree with their political beliefs.
The parents are obvious cowards because what property owner would go out and beat up a kid for tearing down a sign? Sure, they'd probably chew him out and run him off the property but not like the lecture (at a minimum) an adult would get if they tried that same crap.
And yeah... tearing ANY candidates signs down from someone ELSES property is a violation of that property owner's rights.