We live in a democracy, and so we like to believe that that's not the case. And if it were, the free media would soon expose it.
But over the last few years I've seen the evidence mount up disturbingly that it's often true, and the media don't generally seem to talk about it (although they're not entirely mute).
We've seen the rather inept Agent Provocateur trying to incite Plane Stupid to extreme acts. It seems apparent that there are many more less unsubtle agents at work.
I've heard reliable reports from friends at the recent Climate Camp at Heathrow that the police acted heavy-handedly, including deliberately blocking exits and access to emergency vehicles, carefully blocking the TV cameras.
We've heard police, in their own words, "preparing for violence" at peaceful protests.
Today, there are further reports of police aggression at Gay Rights protests (http://snurl.com/57slr). Without wishing to be stereotypical, that's not really a group you picture attacking cops.
Something's gone decidedly wrong.
However, we're now entering the time when everything can be documented and shared worldwide fairly instantly. Text messages have moved on to mobile blogging and twitter with their global audience; worldwide distribution of photos and video (particularly with topical- and geo-tagging) is now possible, and is becoming faster and easier to achieve on the move. The time will come soon when we can see both sides of every protest in real time.
And that's a concept every protester may need to keep in mind these days. Governments (including the UK government) are passing laws to restrict the right to peaceful protest; an essential right which needs to be preserved. We may be at the state where we have to prove our innocence at protests by documenting it on the fly - and prove it not merely to the courts and politicians, but to those members of the public in whose eyes it has been degraded by violent minorities and police aggression.
We don't want another Rodney King situation, but we want the police to know they're answerable.