Kromovaracun
You've raised interesting points, but I think the US model and the UK one are so different as to be not worth comparing.
America's relationship with black America is defined by slavery. Britain's isn't.
Also, when I watch American documentaries, I see far more black American judges, police captains, business leaders etc, than I do (as a proportion of the population) than I do in the UK.
There may be dozens of reasons behind this, but I don't think it's wise to dismiss positive discrimination.
By the way tigerlily11's point is excellent. These ideas normally get put forward by radical think tanks, mainly to test public response, and then quietly filed away once it becomes obvious that the vast majority of people (black and white) are against such endeavours.