Tajfel's minimal group studies assigned people to groups by coin toss, gave the groups meaningless names, and found participants still favoured their own group in allocating rewards. Why is the meaninglessness of the categories the point of the design?

D. Because it strips out every ordinary explanation and finds it anyway.

The design works by subtraction — no history, no contact, no stake, no acquaintance, membership by coin toss — and favouritism appeared anyway. Guard against the overreading: that categorisation is sufficient does not make it necessary, nor real grievances imaginary. It establishes a baseline, and actual conflicts are that pull plus everything else.