Why shouldn't people fight for justice?

Because it hurts and It is also a crime, another thing it can be hard to forgive something for fighting, it is bad for your you sanity, reputation, relationship and self esteem. It's hard to talk to someone you have just beaten up and most of the time you can't make up as they may want to ignore you or come back to get you.

There is this great expression- It takes a bigger man to walk away-