Maybe they thought they were fighting 
    oppression. But at the same time they 
    were oppressing. They became what they 
    claimed to fight.

I see your misunderstanding. You're misunderstanding the terminology. Oppression doesn't simply mean "being mean to people" or "hurting people."

Oppression involves systemic power. Control of the courts, the justice system, the police, the government, of business. Some or all of the above.

Some protestors acted badly! They were wrong! I agree with you! But that is not the same as oppression.