The question of fairness arises whenever someone makes a choice to favor one person or group over another. Paul dealt with the justice of God in doing what He did in this pericope. [source][source][source]
"These verses are a detour from the main road of Paul"s argument. Paul takes this detour because he knows that his insistence on God"s initiative in determining who should be saved and who rejected (see Romans 9:10-13 especially) will meet with questions and even objections. Appropriately, therefore, Paul reverts to the diatribe style, with its question-and-answer format and references to a dialogue partner, that he has utilized earlier in the letter (see Romans 2:1 to Romans 3:8; Romans 3:27-31; Romans 6-7)." [1][source]