Not voting is to preserve the purity of your conscience at the expense of other people's lives

This is a column about why people should vote, however disaffected or pessimistic they may find themselves. But it seems only sporting to my opponents to begin by recalling an occasion on which you could argue that apathy and withdrawal would have been infinitely preferable to democratic involvement. The elections that took place in Germany in September of 1930 were marked by a significant increase in the overall vote - compared with the elections two years earlier, more than 4.5 million extra voters took the opportunity to register their preference, and the party that benefited most from the re-engagement of the young and the habitually indifferent was the Nazi Party. Overnight they went from 810,000 votes to 6.4 million, from 12 seats to 107 (indeed, they were so surprised by their landslide that they didn't even have enough candidates ready to fill the seats). The success provided them with the keys to power.

For the "Don't vote - it only encourages them" school this might seem to be the canonical demonstration of their case. What might have happened if all those don't knows and don't cares had stayed at home, grumbling over the bratwurst about how all the parties were really the same? Surely here is the perfect example of how a vote has no inherent morality in itself (as implied by Tony Blair's alleged remark that it would be better to vote Tory than not at all) and might very well be better left uncast.

But it is possible to look at that grievous election in a different light - to see it as the direct consequence of an earlier indulgence in political disenchantment. What is dangerous about the sanctimonious withdrawal from the political process (and it can be extraordinarily priggish - think of the lofty vanity with which people declare that they can find no one "worthy" of their vote) is not that it marks the death of idealism but the birth of a fantasy about what democratic politics might mean. And that fantasy, as the Nazis discovered, may be more easily satisfied by seductive dreams than by the dull pragmatism of political compromise.

The argument for voting, then, is not that it is somehow magical or noble or even that it is a personally satisfying thing to do. It is not that we have some ritual duty to keep the flame of democracy burning or that by not voting we sully the memory of the war dead. It is precisely the opposite - that it is such a modest and, in some respects, unsatisfying act of discrimination. Burke's celebrated aphorism that "it is necessary only for the good man to do nothing for evil to triumph" really does apply here. However unhappy we are with the choices we have to make, however futile the action feels to us, it remains a deed as opposed to an idle hope. You cross a ballot paper not your fingers.

The refuseniks reply - and it is the least self-regarding of their arguments - that "doing nothing" is not the necessary alternative. They propose an alternative involvement, through single-issue politics or anarchic revolution or even just tending their gardens, activities that they believe will replace the corrupted party politics that has led to their conscientious objection. But even here the argument is illogical. When you exit the polling station you aren't required to sign a pledge that you will undertake no other form of political activity. A vote in a parliamentary election doesn't even disqualify you from working to overthrow Parliament itself. And to refuse to choose now between the disappointing and the disgusting while you wait for something better to come along is to preserve the purity of your own conscience at the expense of other people's lives.

If this week's polls are correct, this may be an academic objection rather than a real one - those withdrawing their vote because they can't find a party which exactly suits them ("it's just not me, you know") can be reasonably confident of which way the result will go (in effect they will allow others to do their dirty work for them). But the electorate has lied before. If, by some ungodly miracle, the Conservatives are re- elected, then some of the poorest people in Britain will have to give up their hopes of a minimum wage - and they would have been left in that predicament by those who claimed to be acting in their name.

I will be voting Labour today - not because I believe they will usher in a New Jerusalem (a new town project that was cancelled along with Clause Four), nor because I found anything congenial in the craven tactical retreats of Mr Blair's campaign (though he has offered me the unusual experience of voting for a politician in the profound hope that he has been lying to the country), nor even because I would particularly want to be identified in anyone's mind as a "Labour supporter", with the whole set of assumptions that follow from the label. I'm voting for Labour because I think they are preferable to the xenophobic, exhausted and morally bankrupt government we have endured for too long.

Only children think of the world as perfect or "all spoiled"; adults have to come to terms with greyer shades of meaning. And while I don't really believe the distinction between Labour potential and Tory actuality is a narrow one, even if it was virtually indistinguishable it would still be worth making a mark in support of the bad rather than the worse. In a rather literal sense it is the least we can do