Christians in Britain and the US who claim that they are persecuted should "grow up" and not exaggerate what amounts to feeling "mildly uncomfortable", according to Rowan Williams, who last year stepped down as archbishop of Canterbury after an often turbulent decade.

"When you've had any contact with real persecuted minorities you learn to use the word very chastely," he said. "Persecution is not being made to feel mildly uncomfortable. 'For goodness sake, grow up,' I want to say."

True persecution was "systematic brutality and often murderous hostility that means that every morning you wonder if you and your children are going to live through the day". He cited the experience of a woman he met in India "who had seen her husband butchered by a mob".

Lord Williams's years as archbishop of Canterbury were marked by turbulence over the church's stance on the role of gay priests and bishops; gay marriage; and homophobia in the wider Anglican communion – with many members of the church expressing disappointment at a perceived hardening in its position on homosexuality.

Asked if he had let down gay and lesbian people, he said after a pause: "I know that a very great many of my gay and lesbian friends would say that I did. The best thing I can say is that is a question that I ask myself really rather a lot and I don't quite know the answer."

Sharing a platform at the Edinburgh international book festival with Julia Neuberger, senior rabbi at the West London Synagogue, Williams launched a withering critique of popular ideas about spirituality. "The last thing it is about is the placid hum of a well-conducted meditation," he said.

He said the word "spiritual" in today's society was frequently misused in two ways: either to mean "unworldly and useless, which is probably the sense in which it has been used about me", or "meaning 'I'm serious about my inner life, I want to cultivate my sensibility'".

He added: "Speaking from the Christian tradition, the idea that being spiritual is just about having nice experiences is rather laughable. Most people who have written seriously about the life of the spirit in Christianity and Judaism spend a lot of their time telling you how absolutely bloody awful it is." Neuberger said she found some uses of the word self-indulgent and offensive. Williams argued that true spirituality was not simply about fostering the inner life but was about the individual's interaction with others.

"I'd like to think, at the very least, that spiritual care meant tending to every possible dimension of sense of the self and each other, that it was about filling out as fully as possible human experience," he said.

Asked by Neuberger whether he felt organised religion encouraged the life of the spirit, he replied: "The answer is of course a good Anglican yes and no". While it can pass on the shared values of tradition, it can also operate as simply "the most satisfying leisure activity possible. It can also be something that you use to bolster your individual corporate ego."

Discussing the relationship between church and state, he said the established church was "an odd business, a very messy and complicated business" but that he was "bloody-minded" about the notion of disestablishment. "I am not in a hurry to see the church disestablished if the pressure is coming from what I regard as the wrong kind of secularism."

On Prince Charles's apparent desire to be known as "defender of faith" (as in all faiths) rather than "defender of the faith" (as in simply Anglicanism) on his accession to the throne, the two clerics disagreed.

Neuberger said she believed "defender of faith" was exactly right. Williams replied: "You're wrong … defender of the faith is just one of those historic titles that is part of the stream of things; it means almost what you want it to mean." Neuberger replied: "What's important about what Prince Charles has said is that it assumes parity of esteem, which for my lot is quite important."

Williams was asked whether the Church of England ran the risk of functioning merely as a well-meaning NGO.

Referring to the current archbishop of Canterbury Justin Welby's recent statements on wanting to compete with payday lender Wonga, he said: "If the church or some of its representatives make remarks on matters of public interest, it can trigger the question where does that come from?

"Can you trace back your attitude to, say, credit unions or the environment to something that is distinctive in the religious heritage? And that means pursuing the conversation a bit.

"The risk of being reduced to an NGO, another woolly, well-meaning liberal thinktank or ambulance service – that's not a fate I would relish for my church," he said.

• This article was amended on 16 August 2013. The original described Julia Neuberger as president of the Liberal Judaism movement. She formerly held that post but stepped down from it when she became senior rabbi at the West London Synagogue in March 2011.