There’s a standard question in ethics — and that’s a fancy way of saying a standard problem in life — when is it okay to do something wrong? When do special circumstances click in and make acceptable kinds of behaviour which ordinarily would be plain bad?

Towards the end of the first Harry Potter film, Hermione knocks out one of her class mates; he’s trying to stop Harry, Ron and Hermione sneaking round the school at night. But they have to stop Voldemort getting the Philosopher’s Stone and becoming immortal.

What’s easy about in adventure film — and hard about life — is the clarity of the greater danger. We know that Voldemort must be stopped at more or less any cost. He’s so totally evil that almost any dubious action would be worth taking if one were attempting to stop him.

It’s just this question that has been raised by a court in the UK where a jury acquitted green activists who had broken into a coal fired power station and caused some damage.

The question is whether a coal-fired power station is so clearly evil that attempting to put it out of use justifies kinds of action that would not normally be acceptable?

The jury’s decision is worrying for several reasons. Firstly: it is not normally considered wrong to plug into the national grid. But if coal-fired power-stations are so obviously a threat to the collective good — so obviously wrong as to justify damaging their property — then it cannot also be morally acceptable to purchase the electricity they produce. In other words, the moral thinking spirals out of control.

Secondly, the evil of any particular coal-fired power-station is not clear cut. There could be too many such power-stations in the world. But it’s not obviously wrong for there to be some coal-fired stations. So attacking one particular station is not legitimate, for its does not identify the correct problem (which is the total number of stations).

Thirdly, what about effectiveness? It seems improbable that activists damaging one power-station will lead to the outcome they hold to be good: a significant reduction in pollution.

There already exists a political process designed precisely to manage large-scale questions of the public good; and even if that operates slowly and imperfectly it seems to be the only plausible way to bring about the kind of change these people want to see. Their action appears to be one of despair — rather than a plausible move to reduce emissions in a significant way.

Logically, the activists don’t seem to have a good case.

The problem for the jury was perhaps quite different. Normally, we expect criminals to have bad intentions: they are criminals because they don’t care enough about other people. The activists seem — on the contrary — to be motivated by care and general good will; so it would be odd to class them with fraudsters and thieves.

I suspect that the jury were in the grip of a “Death of Diana” type phenomenon: that is the view that public institutions are bound to uphold the emotional needs of the population; to be responsive to attitude and feeling, not just to reason and due process.

So the gut instinct is: coal-fired power stations are ghastly — don’t punish people who try to smash them up. As if to say: “I don’t feel these people are really bad, so I’m just not going to find them guilty.”

The intimate notion of badness is given precedent over the details of the law: someone only deserves to be found guilty if they are a bad person. And it’s that issue — rather than the official case (doing a minor wrong to prevent a major wrong) that probably is the significant one.