When to let things let go and when to fight for them?
I think the best message on this topic is the Akkosa Sutta: Insult (SN 7.2) -- about insult and anger:

The first message is that, in order to not accept an insult, don't (violently) reject it, just don't participate in it

And secondly,


  You make things worse
  when you flare up
  at someone who's angry.
  Whoever doesn't flare up
  at someone who's angry
      wins a battle
      hard to win.


For what it's worth I think that my "martial arts" teacher taught just about exactly that same message -- about anger, fighting, and so on.