An analogy...say you worked with someone who was a violent racist, and who had joined in on an attack on a lone Indian bloke on the way home from the office party.
Now let's say he did it five years in a row and kept bragging about it, but on the sixth year, when he tried the same thing, someone else in the office grabbed him by the lapel, and punched his lights out.
Not killing him, just giving him a taste of his own medicine.
At work on the following Monday, would you say,"There was violence on both sides - they're both scum"?
Or would you be organising a whip round to buy the puncher something nice from Hotel Chocolat?