Violence is good television; peace is not. The people who smash things know this. They aren't necessarily natural vandals who would go around breaking windows or setting fire to pallets – though let's not rule that out – but they know the best way to be looked at is to break something. The naughty child in a classroom who always plays up gets the most attention from the teacher, while everyone else working quietly can be ignored.
It's the same reason why terrorists try to blow up aeroplanes rather than organising 200 separate fatal car crashes: one will make the news worldwide, the other will not. Break something, charge a police line, chuck a brick, arrange a colourful stunt – you'll get coverage, while thousands of people can march peacefully along in the background, completely ignored.
News channels think that footage of someone smashing a window or chucking paint at Top Shop are more interesting to their viewers than staring at Ed Miliband's face. They may be right. As Charlie Beckett says, we shouldn't necessarily go blaming the media if the "wrong" messages are taken away from an event by news outlets. The rolling news channels think their viewers are like dozing, elderly, half-blind cats who need a poke in the ribs and a bit of wool dangled in their whiskers before they get interested; they've either hugely miscalculated their audience, or they know them all too well.
The short attention span of the viewer, fingers forever poised over the remote control, demands that excitement be maintained in whatever way is possible. The sight of things being smashed is sexier to look at than tens of thousands of peaceful protesters slowly processing along a prearranged marching route. After a few seconds, you get banner fatigue, and quickly start wondering what's on the other channel.
None of this is a glib dismissal of Saturday's March for the Alternative, or an assertion that it was all a waste of time; the event was a coming together of many different groups with a range of viewpoints, sharing common ground over a way forward that doesn't have to involve the savagery of cuts planned by the coalition government. It was a wonderful show of feeling and determination, and could prove to be a springboard for a wider grass-roots movement. But the difficulty in getting the message across, without having your peaceful protest hijacked by rent-a-mob or having your movement tainted by the actions of unconnected others, is evident.
So what impression are we left with, those of us who didn't attend? Do we think of the thousands of smiling faces, the high spirits, the masses of families and individuals getting together for a shared cause? Or are we left with the sinister fag-end of the day's events – the reports of light bulbs filled with ammonia or fireworks stuffed with coins, the "anarchists" and troublemakers, regardless of what relation they had to the vast majority of protesters?
Where the anti-cuts movement goes from here, and how it conveys its aims, will determine its success. Building a broad grass-roots movement takes time, effort and hard work, most of which is going to happen away from the cameras, away from big events like Saturday's, away from the troubleseekers and troublemakers, too. That's where the battle will be won or lost.