Not worth it.
What if it was you? Or your child?
That's just the way it is.
So, I can fault your argument because it ultimately kills more innocent lives than it saves.
We have criminal trials, and even capital punishment in select cases, in part to prevent people from taking justice into their own hands. Most people can abide occasional errors from a justice system even if that result runs counter to their interests. But if they get to the point that they have NO confidence in it--as where it punishes arbitrarily or never appears to punish at all--then they tend to take matters into their own hands.
An imperfect justice system that strives to get it right is far superior to anarchy and vigilante justice.