Getting involved in politics is a Christian duty," Pope Francis told a gathering of students in Rome in June. "We Christians cannot be like Pilate and wash our hands clean of things." But, according to one strand of opinion, politics is precisely what church leaders should not be doing.

An editorial in the Independent the other day advised the archbishop of Canterbury to stick to matters spiritual, saying that, as someone who has not been elected, he has no business making pronouncements on things political. The example it used was child poverty and welfare reform, arguing that "public pronouncements on purely political issues in which his organisation has no direct involvement are as unconstructive as they are inappropriate".

There are so many things wrong with this it's hard to know where to start. For one thing, no one has elected the Independent's leader writers, yet they make political pronouncements every day. More worrying is the narrow view of politics that is embedded in this idea, as if politics is something that goes on only in Westminster or the town hall or among registered opinion-formers.

When Tony Benn left the House of Commons he declared he did so to concentrate more on politics. Whether you wear a burqa or V for Vendetta mask, politics is how we express our vision of what human life ought to be about. Politics is the way we negotiate our differences. It is a conversation in which everyone has to be involved and where every voice must be heard.

Which is to say: I don't think the church – or anyone else for that matter – requires any special expertise in order to be qualified to take part in the political. Though, as it happens, the idea that the church has no experience to offer when it comes to welfare reform or child poverty is bizarre. There are many places where the church is one of the few remaining social organisations. It was rooted in the fabric of community life long before democratic politics was a gleam in Thomas Rainsborough's eye; for centuries it was the only thing vaguely resembling a welfare state in this country; and it has never abandoned its commitment to universal service provision, if you'll pardon the pun.

The pope learned his politics during Argentina's dirty war, where priests were both victims and collaborators. He re-learned it in the slums of Buenos Aires, trying to put drug dealers out of business. Religion is not just about kissing statues and lighting candles.

Let me be clear. Bishops have no place in the House of Lords ex officio. Religious people ought to have no special privileges simply because they are religious. This makes me a committed secularist. But, by precisely the same token, neither ought they to be denied a voice simply because they are religious.

Yet this is what some people mean when they say that religion ought to be a private matter and that the God-squad should stick to matters spiritual. If the "spiritual" here is being used in opposition to the material, then the spiritual is the one thing the church ought to have nothing whatsoever to do with.The incarnation makes Christianity the most materialistic of the world's great religious traditions. And the opposition of the spiritual and the material was one of the earliest heresies – Gnosticism – that the church condemned. No self-respecting Christian can ever accept this opposition.

Those who think of religion as something to be done only in private by consenting adults haven't ever opened a Bible or understood that free speech is a fundamental principle of democracy. And that means no one needs have a licence to speak out in the public sphere.

Twitter: @giles_fraser