Ramon Llull shifted to hostility only after irenic argument failed

Evidence

The starting point for religious dialogue should not be an attack on the rival religion but a search for a common ground of belief. On this common ground, positive philosophical argument can prove, Llull claimed, the Christian doctrines of the Trinity, Incarnation, and so on, without the need to resort to attacks on Muhammad and the Koran. Real Muslims (or Jews), however, showed little inclination to be converted by his arguments, and Llull gradually adopted a less irenic and more hostile depiction of Islam. — John V. Tolan, Saracens, 76