Should the Christians not be addressed as unbelievers?
QUESTION: Why should we not address the Christians as unbelievers?
ANSWER: We are not obliged to address a blind man as “O blind man!” This would be offensive. Prophetic hadiths prohibit offending non-Muslim citizens of a Muslim country.63
Secondly, the concept of unbeliever has two meanings, one of which is denier of God. We cannot attribute this meaning to the Christians. The other is denier of our Prophet and Islam. This meaning is attributable to them, and they are not offended by this attribution. However, since the concept implies the first meaning, however we use it, it has become an address of offense and insult.
Furthermore, we are not obliged to mix the sphere of belief with the sphere of mutual relations and interaction.
(From Munazarat [“Discussions”])
63 al-Munawi, Faydu’l-Qadir, 6:19.