I can understand it, trisher. Resources for state education are finite. Individuals will try to grab as many of those resources for their own children as possible. Those who work in schools and those who allocate resources have a different perspective and will try, as far as possible, to allocate the resources according to a formula. Those who can afford it will override the system and pay for the resources they want - but only for their own children. The same thing happens with health.
What I don't understand is the obsession with 'bright children'. Education isn't like the Olympics and winning medals, although I have no doubt that competition motivates some pupils. Education should be about encouraging every child to fulfil his/her potential and that's not going to happen when there's an arbitrary cut off point.
Grammar schools weren't invented with the 1944 Education Act, but had existed for many years beforehand, in some cases centuries. The difference was that people no longer had to pay for them or win scholarships. Education beyond elementary level just wasn't available for those who wouldn't/couldn't afford to pay or didn't live in an area where grammar schools existed. The 1944 Education Act made grammar schools free and there was an obligation on local authorities to provide grammar schools in their areas.
It's no wonder that the first generation of free grammar school pupils benefited from them. Life changed after WW2. There was a rise in the number of white collar jobs and there weren't enough grammar school places for the rising number of baby boomer children. The first areas to introduce comprehensive education were the leafy shires, where there were more aspirational parents.
Today's grammar schools are different from the post-war ones, because all children do now have an opportunity for a higher level of education with exams. CSEs weren't introduced until 1965, so before then, secondary modern pupils didn't usually have any accreditation for their years in school and had to go to FE college to take exams (usually vocational). Now every child can take exams when at school.
Nobody's denying that some comprehensives are better than others and/or provide an education suitable for the majority of children they teach. This is a problem where a significant proportion of the most able have been 'creamed off' to go the grammar schools or semi-selective schools which still exist. Sink schools are created and, not surprisingly, few people are happy to send their children to such schools. The demise of local authorities has made the situation worse, because they can't intervene to support sink schools. Meanwhile, some pupils have no choice but to attend them. Grammar schools might provide a solution for the minority, but not for the majority.