You do not stop a tyrant by waggling your finger and telling them to stop. You stop a tyrant by hitting them so fucking hard they never do it again. All of human history shows this, but I suppose a prominent example is Hitler. He conquered, and was allowed to conquer, unopposed, through the entirety of [b]multiple nations[/b], and he didn't stop. Had the western world not decidedly stand up and fight him at a certain point, he would have just kept on going until he went insane or literally steamrolled the world under tank treads.

There have been people who have attacked me for utterly no more reason than to get a rise out of me, or out of boredom, or to try and "win" the favour of someone they look up to or find attractive, or for a hundred other reasons really. I could have just said no and gotten the shit kicked out of me again and again, but I didn't. I stood up to them, and they eventually, one by one, fell away.

Simply put: Bullies are malevolent predators. They prey on the weak. If you don't fight back, they will continue to prey on you as an easy target. That is the hunter mentality. After all, if you're going to pick on someone, who are you going to pick on? The guy who doesn't fight back, or the guy who will bite and kick and punch and spit on you with everything he's got every time you try?

As for abusive parents, that's entirely different and is usually a case by case basis. It's not like a child could possible win a fist fight with an adult in all realism, so this is a lose-lose situation at the best of times.