As was stated, it's called "Vigilantism" and it's generally frowned upon in civilized societies because we believe in the rights to a fair trial, which is not given in this case. As I'm opposed to the death penalty for any number of reasons, I do not agree with it, and there is no guarantee that the person ACTUALLY committed the wrong. I admit there are problems in our judicial system, but I think something like that would only cause a further disintegration, if people begin taking the law into their own hands, then what power does the law possess?