That makes everyone their own judge, jury and executioner.
Sorry but that is wrong on so many levels. You are basically saying that anyone can take justice into his own hands if he thinks the authorities aren't doing enough? that is an extremely slippery slope and not in accordance with the last of the Sheva Mitzvos Beney Noach.
I would like to add that the Torah agrees to the concept of becoming j/j/e in
certain scenarios. Pinchas is a fine example Another example is in last weeks parsha- haba bemachteres.
Personally, I find the idea of when its acceptable to become your own j/j/e to be pretty complex. Movies such as Boondock Saints confront the issue, showing both sides of the coin, leaving the viewer to decide whether the main protagonists are evil, wrong or neither.