Yeah, this can be a tough one. Withdrawing from aggression can be a good thing, but then again there are times when non aggressive self assertiveness is the order of the day.

Balance is key, but difficult to practice and it takes weighing things up, often very quickly before having to make a decision which road to take.
This is where mistakes can get made.

I also think life is short and there are people who have views and opinions that I know will never change their minds about, so it's a waste of my energy to even bother trying to do so (unless they are in immediate danger, etc. of course).