I thought the film was a masterpiece, while Rebecca did not like it at all. We bickered all the way home to Brixton, Rebecca trenchantly repeating that violence could never, ever be condoned, and me dogmatically reiterating that the film wasn't necessarily concerned with justifying violence - though it was certainly possible that it might be - but was hugely valuable in its explanation of how, given certain conditions, uncomfortable and unfair situations will inevitably breed physical manifestations of frustration and rage. The film should not be condemned because it ended in violence, it should be applauded for offering a meticulous dissection of the social mores which foster the violent disorder that we couldn't deny was happening all around us.
Except that the discussion wasn't quite that civilised. I became angrier and more aggressive in my exhortations until at last Rebecca stopped me in my tracks. White-faced, she started hissing at me to calm down. This had gone too far. Everyone on the bus was looking at us. I was hurting her.
I realised that I'd been grabbing at her wrist so hard that there were red weals appearing round it. No wonder I could see how bad feeling as depicted in Do The Right Thing could escalate into violence. I was capable of resorting to violence just to ensure that my reading of a movie was the one that prevailed during the post-screening deconstruction.
Then as now, I was shocked at my own behaviour, but also struck by the incident's perfect symbolism. While it was a living illustration of my own argument, it was at the same time the most apposite vindication of Rebecca's view that she could have wished for. When passions run high, it is easy for situations to get out of hand. Once that has happened, the person who resorts to violence has lost the moral high ground, regardless of the merits of their viewpoint.
Although I resent the fact that if I were inclined to visit Stonehenge to watch the sun rise at the summer solstice I would not be able to, the pictures from early yesterday morning scarcely give the impression that a trip to this ancient site would be a tranquil and spiritual experience. The people clambering over the stones and lolling about on top of them suggest that, despite all their protestations, this world heritage site does need to be protected from the tender mercies of the rag-bag of vulnerable innocents, charismatic troublemakers and disturbed drop-outs who have become known as new age travellers.
And while I feel no empathy with the pagans and druids who this year were granted access to the stones for a morning of neo-neolithic play- acting, I do think it's a shame that their hard-won, though mildly barking, right to fart about in robes during the Stonehenge solstice has been thwarted.
It would have been a fine thing if their cod ceremonies could have gone off without incident, not for their own sake but because it could have been the beginning of a detente around Stonehenge, paving the way towards a less authoritarian protection of the standing stones. Instead, violence has as usual achieved the very opposite result to the one that was aimed for. The eco-warriors who wish to gain access to the site have simply proved that they - just like any other ravaging group in history - are fighting to gain control of land for no higher purpose than to see their own will prevail.
Coming as it does in the wake of the more serious disturbance in the City of London last Friday, this outbreak of violence will be read as more evidence that the only alternative to the neo-liberal tyranny, which is all that mainstream politics has to offer, is chaos and anarchy. Again the marginal have marginalised themselves yet further. Again protest has been overshadowed by violence.
That is a pity, because the various issues at the heart of the Carnival Against Capitalism are issues we should all be engaged with. We should cancel world debt, we should reject the dominance of the car and we should turn away from the exploitative jungle law of global capitalism, and not just because a bunch of cranks, anarchists and eco-warriors with more temper than sense fancy it will make a fairer, tidier world.
I feel frustration and rage myself that all of the humanity and caring that was on display in the City last Friday has been squandered. While it has become a modern mantra to to deplore the way in which otherwise peaceful protests are so often marred by violence, the truth is that its is only the violence that we ever hear about. The protests themselves are discussed only as an adjunct to the main event.
While we're used to hearing about small groups of troublemakers determined to disrupt peaceful protest, we hardly ever ask ourselves why this keeps happening. Why do so many benign alternative organisations become magnets for people bent on destruction? How can a protest that starts with such style end with such bitterness? And, in the case of the Carnival Against Capitalism, why is it that the organisers actually wanted trouble, at least in so much as they would not cooperate with the police.
The answer again is rage and frustration. Peaceful protest, unless it takes place on a massive scale, is not newsworthy, while violent protest is. The people who took part in Friday's demonstration do stand for important issues, issues with which mainstream politicians are willing to become engaged in only the most desultory of ways. Even the hate-crazed agents provocateurs of Class War care, perhaps more than their ability to express themselves allows them to communicate in civilised terms.
While there has been much lip service paid to the idea that these are the days of "single-issue activism", "cranky extremism" or "eco-wars", there is not much acknowledgement of the reasons for this. People become obsessed with single issues because they sense that there is no give in the system, no way for them to get across a message that they believe in with passion. Their extremism is fostered by their inability to make any impact in the mainstream.
So many people, so soon into the Labour Government they wanted for so long, now face the prospect of remaining unrepresented by any government at all in their lifetime. Tony Blair has made it clear that it is not his job to listen to us, but our job to listen to him, to the extent that he casually instructed his MPs to spend less time doing their jobs - representing their constituents - and more time supporting his government. No wonder these passionate young people feel frustrated, with so much they want to tackle and no political party for them to join or even to support.
The violence on Friday and to a much lesser extent the violence on Monday morning is not excusable, but it is understandable. Whole swathes of people are disenfranchised not by poverty or social exclusion but by the narrow vision of life on the planet which is encouraged by our febrile love affair with the great god money.
The clash between politics and people has never been more violent, or more extreme. And that, not a bunch of crusties smashing up McDonald's, is what's going to end up hurtling us all into anarchy.