Does not the argument that God permitted kindness and good treatment towards disbelievers who do not wage war contradict His, the Almighty's, saying: "O you who have believed, do not take your fathers and your brothers as allies if they have preferred disbelief over belief"?

The interpretations mentioned by the questioner to reconcile the meaning of the verse: "Indeed, Allah only forbids you from those who fought you because of religion and expelled you from your homes and aided [others] in your expulsion - that you make allies of them. And whoever makes allies of them - then it is those who are the wrongdoers" (Quran 60:9), with the explicit meaning of the verse: "O you who have believed, do not take your fathers and your brothers as allies if they have preferred disbelief over belief. And whoever does so among you - then it is those who are the wrongdoers" (Quran 9:23), are all plausible.

The most probable interpretation is that what is forbidden is preferring the love of these fathers and brothers over the love of Allah and His Messenger, as stated in the verse that follows: "Say, [O Muhammad], 'If your fathers, your sons, your brothers, your spouses, your kindred, the wealth you have gained, the merchandise in which you fear stagnation, and dwellings with which you are pleased are dearer to you than Allah and His Messenger and striving in His cause, then wait until Allah executes His command.' And Allah does not guide the defiantly disobedient people" (Quran 9:24). This is supported by what the questioner quoted from Sheikh Ibn Uthaymeen: that affection (mawaddah) is one thing, and natural love for relatives is another, and that what is prohibited is preferring the love of anyone other than Allah over the love of Allah and His Messenger.

Therefore, the criterion for forbidden affection towards disbelievers is preferring their love over the love of Allah and His Messenger.