From another perspective, I know how it feels to be angry at someone. I also know how it feels to be wronged by somebody and the human thing to feel towards someone that we believe has wronged us is for that person to get what's coming to them (like some people in the wt for instance to some people) - and we don't need to hear what supporters or sympathysers of the such (someone like me) have to say, it makes us angry at the supporter for not backing us up. I have been there and I understand.
But if anyone embarks on personal vengeance and feels he is justified in breaking the law, that person is making a serious mistake and could pay dearly.
God is just and he will not allow those that have been wronged to go un-avenged. Also, taking things into your own hands is not the same as justice from God aka ironic justice (or vengeance, call it what you like). And just as long as you are friends with God, he will back you up even if you are partially in the wrong. If you get angry with God, it's like cutting off your nose to spite you face. And if a person defiantly fights against God or against his friends....we'll see what happens.