But does Islam really promote friendships with non-Muslims? Not according to the Qur'an, as Robert Spencer and I show in this discussion with Pastor Joseph:
For those who'd like the relevant sources, here you go:
Qur'an 3:28—Let not the believers take disbelievers for their friends in preference to believers. Whoso doeth that hath no connection with Allah unless (it be) that ye but guard yourselves against them, taking (as it were) security. Allah biddeth you beware (only) of Himself. Unto Allah is the journeying.
Ibn Kathir on 3:28—Allah said next, (unless you indeed fear a danger from them) meaning, except those believers who in some areas or times fear for their safety from the disbelievers. In this case, such believers are allowed to show friendship to the disbelievers outwardly, but never inwardly. For instance, Al-Bukhari recorded that Abu Ad-Darda said, "We smile in the face of some people although our hearts curse them." Al-Bukhari said that Al-Hasan said, "The Tuqyah is allowed until the Day of Resurrection."
Qur'an 5:51—O you who believe! do not take the Jews and the Christians for friends; they are friends of each other; and whoever amongst you takes them for a friend, then surely he is one of them; surely Allah does not guide the unjust people.
Ibn Kathir on 5:51—Allah forbids His believing servants from having Jews and Christians as friends, because they are the enemies of Islam and its people, may Allah curse them. Allah then states that they are friends of each other and He gives a warning threat to those who do this, (And if any among you befriends them, then surely he is one of them.) Ibn Abi Hatim recorded that `Umar ordered Abu Musa Al-Ash`ari to send him on one sheet of balance the count of what he took in and what he spent. Abu Musa then had a Christian scribe, and he was able to comply with `Umar's demand. `Umar liked what he saw and exclaimed, "This scribe is proficient. Would you read in the Masjid a letter that came to us from Ash-Sham'' Abu Musa said, `He cannot.'' `Umar said, "Is he not pure'' Abu Musa said, "No, but he is Christian.'' Abu Musa said, "So `Umar admonished me and poked my thigh (with his finger), saying, `Drive him out (from Al-Madinah).' He then recited, (O you who believe! Take not the Jews and the Christians as friends...).