I'd agree with you, except that police harassment is used to stifle dissent, often. There's an activist in Montreal (Canada, not an oppressive militant dictatorship) by the name of Jaggi Singh. In a city where jaywalking is illegal, but the norm, he has been given citations, and apparently also beaten in the process, several times. For giving speeches at protests, he has been arrested on charges of "inciting a riot."
Protesters at summits often face pepper spray and attack dogs. "Free speech zones" are not. Beyond this, though, minorities often face prejudice at the hands of the police - imagine how your life would be, if every time you drove to your high-paying job, you were stopped by the police because they didn't believe you could possibly own that nice a car.
The police don't really care about what's right and wrong; they care about enforcing order. Order favours the status quo. When police are given new powers, and this extends to powers that fundamentally breech citizens' rights to privacy, they invariably abuse them in order to maintain the status quo. We can't tolerate this in a civil society.