Edward Woollard was a bloody idiot who could well have killed somebody. However, this should not mean that he should be tried and punished unfairly; there is no reason for English justice to be a bloody idiot, too.
However, to begin with, one thing must be made clear. There can be no sensible excuse for what he did with that fire extinguisher. In the words of the Guardian :
[Woollard] was seen picking up the half-empty canister, discarded by another student, before spraying the crowd below and then throwing it in the direction of police beneath. Other footage showed it hurtling from the roof to land with a heavy, audible thud within a metre of police officers.
This is the sort of case where there should be criminal liability. There even seems good reason to give a custodial sentence. However, Woollard was sentenced to an incredible 32 months of imprisonment. This seems harsh and disproportionate in respect of an impulsive action where (thankfully) no one was actually injured.
Strictly speaking, Woollard was not even directly prosecuted for the fire extinguisher incident. The charge, as supplied by the Crown Prosecution Service, reads more generally:
Edward Woollard, on 10 November 2010 at Milbank Tower, London SW1, used or threatened unlawful violence when present together with others, being three or more persons in total, who used or threatened unlawful violence, and the conduct taken together was such as would cause a person of reasonable firmness present at the scene to fear for his or her personal safety, contrary to Section 2 of the Public Order Act 1986 .
Without wishing to diminish the seriousness of what Woollard did, is there a question about whether this was actually the correct offence with which to charge and prosecute him? Was this really a Section 2 offence, with its onerous range of possible sentences?
The offence of "violent disorder" requires there to be three or more individuals threatening unlawful violence, although not all of them need to be charged or identified. It is not an offence that should be prosecuted in respect of a discrete act by one individual. After all, it was only Woollard who dropped a fire extinguisher from Milbank Tower.
Perhaps significantly, the CPS has now confirmed that no other person has been charged in respect of violence at Milbank Tower, only Woollard. But unless there were others engaged in "violent disorder," the Section 2 offence simply does not seem to apply, however incredibly stupid the particular action.
Can one be concerned that this offence was chosen because the range of custodial sentences available to the sentencing court would be higher than another offence that dealt with his individual actions? It must be noted that Woollard had given himself up and had indicated that he would plead guilty. It was thereby unlikely he or his lawyer would object to the then offence selected.
The Section 2 offence is usually used for mass pub fights or incidents involving football hooligans. Often there is an element of planning, or there are serious knock-on effects: a group throwing missiles or having a punch-up. (See these examples with similar sentences put together here  by @MTPT  on Twitter.)
It is clear that Woollard did not plan to drop the extinguisher: it was an impulsive, if dangerous act. As Deborah Orr says  in the Guardian:
He was a schoolboy who had came up on a coach from the New Forest to attend a protest organised by the National Union of Students (NUS), and there is no sign that he was expecting to be caught up in a breakaway riot that day. He wore no hood. He wore no mask. He had brought no billiard balls. He didn't even liberate the fire extinguisher in the first place.
However, in passing judgment, Geoffrey Rivlin, QC told Woollard that he was "exceedingly fortunate" his action did not result in death or severe injury to others, as it was a case of "serious criminal violence creating a situation of grave danger to others".
[T]he right of peaceful protest is a precious one. Those who abuse it and use the occasion to indulge in serious violence must expect a lengthy sentence of immediate custody.
In respect of Woollard's intentions:
[His main motivation] was to create a sense of disturbance, anarchy and antisocial behaviour.
The judge then turned to the sentence to be passed:
It is deeply regrettable, indeed a shocking thing, for a court to have to sentence a young man such as you to a substantial term of custody, but the courts have a duty to provide the community with such protection from violence as they can, and this means sending out a very clear message to anyone minded to behave in this way that an offence of this seriousness will not be tolerated.
If ever a case calls for a deterrent sentence, this is it. I wish to stress, however, that this is not a case of making an example of you alone. Anyone who behaves in this way and comes before the courts must expect a long sentence of custody.
Was this the correct approach? Or was it unjust?
A "deterrent" sentence is one, by definition, that is disproportionate to the offence committed but has been imposed for wider policy reasons: so as to have an effect on others.
However, justice requires that a convicted defendant be treated similarly to another person convicted of the same crime, unless there is a good reason to depart from a consistent approach.
There is no reason for violent disorder at a political demonstration to be more worthy of a deterrent sentence than a fight outside a public house or an attack by a racist gang. It is in the nature of Section 2 offences that they will tend to be in respect of disturbances that have a communal or social context.
A disproportionate sentence really serves the interests of no one. It does not assist the court in making the supposed "example": for if it is overturned on appeal, then any force of deterrence is lost.
It does not serve the public, as it can suggest to those who plan disorder that one mayas well "be hanged for a sheep as for a lamb".
It will not deter actions similar to those of Woollard, as the sentence has been given in respect of something evidently done on impulse.
And it certainly does not assist in the rehabilitation of an 18-year-old offender, whose life is now ruined.
Rather, this is the very type of conviction and sentence that may tend to undermine the legitimacy of the state and its administration of justice. It appears that although Woollard was a bloody idiot, this could well be the wrong offence and the wrong sentence.
And, if this is so, then by seeking to make an example of him the court, perhaps, has itself set the bad example.
David Allen Green is legal correspondent of the New Statesman .