Talking in a prison library not so long ago, I was startled to learn of the prisoners' favourite writer. Almost all of them read, liked and believed the work of David Icke, the former goalkeeper who has said that he is the son of God, that senior politicians are satanic paedophiles, and that the world is ruled by lizard-humans, who include George W Bush, the late Queen Mother and, more mysteriously, Kris Kristofferson.

It was surprisingly difficult to make the case against Icke. I sensed that, listening to me, the prisoners had already decided that I was a lizard, and that my argument was simply more lizard-talk. Besides, a belief system in which power rests in the hands of a mindless, scaly elite seemed to suit their situation.

Right now, they might have a point. A ruling by the European Court of Human Rights has united Britain's normally factional political and media classes, turned Jack Straw and David Davis into brothers-in-arms, and caused the mighty choir of press and online moralists to sing with one voice. This almost unprecedented level of accord has been prompted by the suggestion that the British Government – and others in Europe – should clarify whether prisoners have a constitutional right to vote in elections.

The Prime Minister has confessed that the mere thought of convicts voting makes him "physically ill" – quite a claim. He is in charge of a government which likes to claim that over the past decade the state has "abused and eroded fundamental human freedoms and historic civil liberties". He can oversee the loss of hundreds of thousands of jobs, know that more young people are out of work than ever before, slash and burn his way through the welfare system, turn a blind eye to the closure of libraries across the country, and maintain throughout a plump smile on his smooth, rosy features.

Yet the idea that criminals should play a part in democracy apparently risks a nasty mess all over the carpet of 10 Downing Street. Disingenuously, those who argue against the voting rights of prisoners have invoked that old favourite, the danger posed by unelected European judges to the British Parliament. At heart, though, their argument is not about sovereignty but about the right to punish. Those who have done wrong, they believe, have forfeited their most basic democratic right.

It is faintly alarming to hear politicians discussing who should be allowed to vote for them and who should be excluded from the process. Once democracy becomes conditional upon the good behaviour of citizens, it is fatally compromised. As soon as a general principle is in place which sees law-breakers deprived of their right to vote, it can be modified at will by politicians.

Why not, for example, deprive a convicted criminal of the right to vote for the rest of his or her life, as happens in some parts of the world? Perhaps certain crimes should automatically invoke a democratic penalty, and those crimes could be changed over time to reflect the mood of the moment. Democracy is not an easy system – it involves giving a voice in society to those many of us would prefer to remain silent – but the current clamour on behalf of decent, law-abiding citizens is in reality atriumph for a bullying, tabloid morality over logic, decency and forgiveness.

Kenneth Clarke, the Justice Secretary, was on the right track when he attacked the "bang 'em up approach" to prison. Locking up people without seeking to change them was, as he said, "what you would expect from Victorian England". It is the reason why reoffending rates among released short-sentence prisoners has been on the increase.

How strange it is that the same note of common sense and sympathy is not heard in the debate about prisoners' voting rights. If justice is to include, along with punishment, the prospect of some sort of reparation, it is right to allow those inside a small but important stake in the society outside, as represented by the ballot box.

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