A quota system? I would love to see verifiable evidence that such a thing exists. Positive discrimination only happens in certain regulated areas and would not have been in place when staffing a space launch!
What I do see is that as soon as the long-standing white, male, middle-class hegemony is challenged even slightly there is an outcry from those who feel threatened at the idea that they will have to compete on a meritocratic level instead of being the automatic default choice.
None of this is relevant to the Sainsbury's ad, however. All that is doing is using a happy, functional family to create a feeling of goodwill at Christmas in the hope that shoppers will associate that feeling with their supermarket. The colour of that family's skin is irrelevant to the message, and anyone who feels threatened by it (or aggrieved, or resentful) should perhaps take a step back and wonder why.