The Institute of Ideas think-tank has accused fellow secularists of engaging in a "New Atheist witch-hunt" over the Pope's upcoming British visit.
They say that the tenor of the criticism of the pontiff and the Catholic Church "is in stark contrast to their own professed views on tolerance."
Speaking to launch a series of religion-themed debates at the Institute's annual festival, director Claire Fox, a regular on BBC Radio 4's 'Moral Maze' programme, declared: "While many reacted with horror at France and Belgium with their intolerant ban on the burqa, the response of some secular campaigners shows that such demonisation of religious groups is alive and kicking in the UK."
Ms Fox accused anti-visit campaigners of making "hysterical, oft-repeated arguments" such as that the Pope is “leader of the world’s largest paedophile ring”. She said these "have more in common with contemporary heresy-hunting than the free-thinking spirit of Enlightenment secularism."
Fox continued: "There are many reasons to criticise religious leaders, and plenty are coming from within the Church itself, but secularists really should take the opportunity to remind themselves of the Enlightenment values they claim to stand for – such as tolerance, freedom of thought and conscience and a human being as a rational subject - rather than focusing on what they hate about the Church and, by extension, Catholics."
The Institute, which emerged from a far-left background but now espouses combatively libertarian ideas, says that there is a need for a "more clear-thinking and rational debate on the role religion plays in a secular society". This will be one of the topics at its 'Battle of Ideas' festival (www.battleofideas.org.uk) over the weekend 30-31 October at the Royal College of Art in London.
A debate on 'The Catholic Church: more sinned against the sinner?' will feature Catholic-born humanist lawyer John Fitzpatrick, US-based libertarian commentator Wendy Kaminer, philosopher Peter Cave and Catholic commentator Austen Ivereigh.
Leaders of the Protest the Pope coalition (http://www.protest-the-pope.org.uk/) have argued that they are not anti-Catholic, but are opposed to the views of the present Pope and to the status and cost of an official State Visit.
Terry Sanderson, president of the National Secular Society, said: "The cost of this visit to the taxpayer will run into tens of millions of pounds, at a time when the Government is about to announce 25 per cent cuts in public spending. If the Pope really cared about poverty - and these Government cuts will hurt the poorest in our society - he would offer to pay his own way from his Church’s fantastic wealth."
A press conference is being held by the group at 3pm on Tuesday 14 September, at Conway Hall in central London, to further outline its protest plans and its charges against Pope Benedict.
Speakers include the feminist writer Joan Smith, Terry Sanderson, President of the National Secular Society, Andrew Copson, Chief Executive of the British Humanist Association and Marco Tranchino and Peter Tatchell of the Protest the Pope campaign.
Mr Tranchino said: "On Saturday 18 September we will assemble at 1.30 pm at Hyde Park Corner, march through central London and conclude our protest with a rally opposite Downing Street. We will tell our Government that it should not honour the Pope as a Head of State. The Vatican must not be allowed to consolidate its influence. In a liberal society, no religious leader should be permitted to attack our equality laws without challenge and no religious leader should have privileged, undemocratic influence on our political leaders."
Progressive Catholic (http://www.catholic-womens-ordination.org.uk/links.htm) and Christian groups have largely steered clear of the coalition, but are working actively to promote alternative, religiously- and theologically-grounded perspectives on key issues such as women's ministry, the acceptance of lesbian and gay people in the church, family planning, human rights, HIV-AIDS prevention and other concerns where Benedict XVI has pursued hardline policies and rhetoric.
Opinion polls, including one commissioned by Bible Society funded think-tank Theos, are indicating that the majority of the public are not especially interested in the Papal visit.
The BBC has announced that it will have a total of 400 staff covering the four-day Papal visit, which begins on Thursday 16 September.
The results of the latest CVR-ITV survey have particularly impressed Bernard Wynne of the Stand Up For Vatican II network (http://www.standup4vatican2.org.uk/), who says: "Our experience in a range of Catholic reform organisations confirms our belief that around 50 per cent of Catholics in the UK broadly support the reform agenda."
"On some issues however, this survey suggests that the percentage is much higher, for example the number supporting a married priesthood is well over 60 per cent. The response regarding gay relationships indicates that a high percentage of respondents support more tolerance in respect of celebrating such relationships."