"Revenge is a dish best served cold." ~multiple sources/origins
Retaliation seems to be a human thing. We're the only life form that does it on the planet. I don't mean by defense because that's different. Hurt someone and hours/days later they come back and do something in return just as nasty.
Control is what dictates a civilized human being. That and staying with the law(s) whatever they may be depending upon where you live. Having the control not to strike back shows maturity and civility.
As Martialist we train to inflict damage upon the human body. The why's are up to us, no? Thus the deeper we get into our individual arts the more control we are supposed to have. This is control extends to the mental and emotional as well as the physical. We should be maturing as human beings the further along we get into our arts. Retaliation and revenge is something kids do, the immature, the insane and disturbed.
This is why we have that 7-14 day waiting period when we want to buy a hand-gun. This is why we have the police and other LEO's to handle the situation should it be an assault on person or property. This is why we have the military to help defend against incursions into our homeland.
George Lucas wanted to call his third installment of the original Star Wars trilogy "Revenge of the Jedi" but fans said that "Revenge" is not a Jedi thing to do...thus he changed it to "Return." Now the third prequel is called "Revenge of the Sith" and no one is throwing up any guff on that. Naturally, the Siths are the
bad guys.
Back on earth, we should be well aware of the things that we can do to another human being and the effect it has on them. We should also be aware of the effects it will have on us afterwards. Will we feel better because we got back at them? Will it make is better people? Will it make us better martial artists? If we're instructors (and I'm
NOT 
) how would this revenge mind set sit with (your) students?
We learn combative forms so that we will have no fear from our fellow man should he attack us. In the moment of attack we will/should defend. If one of our own is injured/attacked and we are present then we will/should defend. Going back later is revenge and not a true martialist's way.
On Karma, well if it is true then we should allow it to work it's way when it's time. For those who believe in (the Christian) God then trust Him to take care of it in His time. Otherwise call the cops and let them take care of it, where applicable.