It may not be to your taste, but the fact that those flats sell for millions today is a counterexample to your claim that brutalism is nothing more than an assault on the lower class. The fact is that plenty of wealthy people disagree with your aesthetic judgement enough to pay to live in those flats for sums that would easily buy them a house in a leafy, conveniently commutable part of London. It provides an alternative motive for at least some brutalist designs.