At some point they do.
If a guy tries to mug you and you beat the piss out of him, yea, he had that coming and there's no right to complain about anything.
If a guy tries to mug you, and you beat him to death on the street, grab his ID, find his home, break in, tie up his wife, round up his children and starts brutally torturing the children to death in front of the mother and then after all the children are dead he takes the wife and as he's raping her he cuts off her head with a steak knife he found in the kitchen and then sets the severed head on a spike in the now destroyed families lawn....yea I'd say that the person being mugged crossed a line and wronged the mugger.