Last night I was arrested in my home town, outside an event to which I had been invited, for standing lawfully on the sidewalk in an evening gown.

Let me explain; my partner and I were attending an event for the Huffington Post, for which I often write: Game Changers 2011, in a venue space on Hudson Street. As we entered the space, we saw that about 200 Occupy Wall Street protesters were peacefully assembled and were chanting. They wanted to address Governor Andrew Cuomo, who was going to be arriving at the event. They were using a technique that has become known as "the human mic" – by which the crowd laboriously repeats every word the speaker says – since they had been told that using real megaphones was illegal.

In my book Give Me Liberty, a blueprint for how to open up a closing civil society, I have a chapter on permits – which is a crucial subject to understand for anyone involved in protest in the US. In 70s America, protest used to be very effective, but in subsequent decades municipalities have sneakily created a web of "overpermiticisation" – requirements that were designed to stifle freedom of assembly and the right to petition government for redress of grievances, both of which are part of our first amendment. One of these made-up permit requirements, which are not transparent or accountable, is the megaphone restriction.

So I informed the group on Hudson Street that they had a first amendment right to use a megaphone and that the National Lawyers' Guild should appeal the issue if they got arrested. And I repeated the words of the first amendment, which the crowd repeated.

Then my partner suggested that I ask the group for their list of demands. Since we would be inside, we thought it would be helpful to take their list into the event and if I had a chance to talk with the governor I could pass the list on. That is how a democracy works, right? The people have the right to address their representatives.

We went inside, chatted with our friends, but needed to leave before the governor had arrived. I decided I would present their list to his office in the morning and write about the response. On our exit, I saw that the protesters had been cordoned off by a now-massive phalanx of NYPD cops and pinned against the far side of the street – far away from the event they sought to address.

I went up and asked them why. They replied that they had been informed that the Huffington Post event had a permit that forbade them to use the sidewalk. I knew from my investigative reporting on NYC permits that this was impossible: a private entity cannot lease the public sidewalks; even film crews must allow pedestrian traffic. I asked the police for clarification – no response.

I went over to the sidewalk at issue and identified myself as a NYC citizen and a reporter, and asked to see the permit in question or to locate the source on the police or event side that claimed it forbade citizen access to a public sidewalk. Finally a tall man, who seemed to be with the event, confessed that while it did have a permit, the permit did allow for protest so long as we did not block pedestrian passage.

I thanked him, returned to the protesters, and said: "The permit allows us to walk on the other side of the street if we don't block access. I am now going to walk on the public sidewalk and not block it. It is legal to do so. Please join me if you wish." My partner and I then returned to the event-side sidewalk and began to walk peacefully arm in arm, while about 30 or 40 people walked with us in single file, not blocking access.

Then a phalanx of perhaps 40 white-shirted senior officers descended out of seemingly nowhere and, with a megaphone (which was supposedly illegal for citizens to use), one said: "You are unlawfully creating a disruption. You are ordered to disperse." I approached him peacefully, slowly, gently and respectfully and said: "I am confused. I was told that the permit in question allows us to walk if we don't block pedestrian access and as you see we are complying with the permit."

He gave me a look of pure hate. "Are you going to back down?" he shouted. I stood, immobilised, for a moment. "Are you getting out of my way?" I did not even make a conscious decision not to "fall back" – I simply couldn't even will myself to do so, because I knew that he was not giving a lawful order and that if I stepped aside it would be not because of the law, which I was following, but as a capitulation to sheer force. In that moment's hesitation, he said, "OK," gestured, and my partner and I were surrounded by about 20 officers who pulled our hands behind our backs and cuffed us with plastic handcuffs.

We were taken in a van to the seventh precinct – the scary part about that is that the protesters and lawyers marched to the first precinct, which handles Hudson Street, but in the van the police got the message to avoid them by rerouting me. I understood later that the protesters were lied to about our whereabouts, which seemed to me to be a trickle-down of the Bush-era detention practice of unaccountable detentions.

The officers who had us in custody were very courteous, and several expressed sympathy for the movements' aims. Nonetheless, my partner and I had our possessions taken from us, our ID copied, and we were placed in separate cells for about half an hour. It was clear that by then the police knew there was scrutiny of this arrest so they handled us with great courtesy, but my phone was taken and for half an hour I was in a faeces- or blood-smeared cell, thinking at that moment the only thing that separates civil societies from barbaric states is the rule of law – that finds the prisoner, and holds the arresting officers and courts accountable.

Another scary outcome I discovered is that, when the protesters marched to the first precinct, the whole of Erickson Street was cordoned off – "frozen" they were told, "by Homeland Security". Obviously if DHS now has powers to simply take over a New York City street because of an arrest for peaceable conduct by a middle-aged writer in an evening gown, we have entered a stage of the closing of America, which is a serious departure from our days as a free republic in which municipalities are governed by police forces.

The police are now telling my supporters that the permit in question gave the event managers "control of the sidewalks". I have asked to see the permit but still haven't been provided with it – if such a category now exists, I have never heard of it; that, too, is a serious blow to an open civil society. What did I take away? Just that, unfortunately, my partner and I became exhibit A in a process that I have been warning Americans about since 2007: first they come for the "other" – the "terrorist", the brown person, the Muslim, the outsider; then they come for you – while you are standing on a sidewalk in evening dress, obeying the law.