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Problems with traditionalists

In addition to all the criticism from those demanding modernisation, some traditionalist Catholics denounced him as well. These issues included demanding a return to the Tridentine Mass, as well as the repudiation of reforms instituted after the Second Vatican Council, such as the use of the vernacular language in the formerly Latin-language Roman Rite, ecumenism, and the principle of religious liberty. In 1988, the controversial traditionalist Archbishop Marcel Lefebvre, founder of the Society of Saint Pius X (1970), was excommunicated under John Paul II because of the unapproved ordination of four bishops, which Cardinal Ratzinger called a "schismatic act".

The World Day of Prayer for Peace, with a meeting in Assisi, Italy, in 1986, in which the pope prayed only with the Christians, was criticised for giving the impression that syncretism and indifferentism were openly embraced by the Papal Magisterium. When a second Day of Prayer for Peace in the World was held in 2002, it was condemned as confusing the laity and compromising to false religions. Likewise criticised was his kissing of the Qur'an in Damascus, Syria, on one of his travels on 6 May 2001. His call for religious freedom was not always supported; bishops like Antônio de Castro Mayer promoted religious tolerance but at the same time rejected the Vatican II principle of religious liberty as being liberalist and already condemned by Pope Pius IX in his Syllabus errorum (1864) and at the First Vatican Council.