The case has some plausible reasoning underlying it. If some people lack the advantages that others have, we could compensate for that by lowering the standards that people from deprived backgrounds are required to meet. For example, if it takes 3 passes at A* level to gain university admission, we could lower that to an A and 2 Bs for those whose poorer backgrounds and schooling gave them less chance of achieving those 3 A*s. It might be as hard for them to secure ABB than it is for their more affluent counterparts to secure 3 A* passes.
On the down side of this is the fact that we would be admitting people with lower qualifications to university, lowering the overall quality of the graduates produced. Given a choice, most people would choose to be operated on by the surgeon who gained 3 A*s than by the one for whom allowances were made to compensate for their background. If UK universities were to admit people with lower qualifications, their standing in world rankings would decline against those which admitted on merit.
There is also a view that a pass should indicate performance, not effort. We are more interested in the level attained than in the moral virtue of those who strive to attain it. Affirmative Action is opposed by many on this very principle. Someone should be in a job, they say, because they merit it, not because their cultural or ethnic background should allow them in with lower qualifications. If those backgrounds do indeed make it harder for people from them to qualify, the effort should be made to redress that fact, not to lower the qualifying level for some groups. The aim should not be to lower the bar, but to ensure that as many as possible can reach it, regardless of their background.
Some backgrounds are harder than others to rise up from, so the effort should be put into making it less hard, into identifying merit where we can, and in beating a pathway before it so people can rise up on merit without needing any special consideration. This is undoubtedly harder to do than simply lowering standards, but it does lead to a higher level of excellence that more talented people can aspire to attain.