Academic selection is fair. It enables students to be able to learn with other students which are of the same ability, so that less able students do hinder the ability of the other students to learn. I went to a grammar school, and even there there was a broad ability grade, there were people who got D's at GCSE and people who got all A*'s, the same could be said for a-levels/IB. It was also a common rule, that the people who disrupted classes and held them back were often, hard to believe, underachievers who made it even harder for people to progress. And when the school further streamed classes after GCSE, there was a much better education environment with people of the same ability.
If grammar schools are achiving as well as similar comprehensives, then sure, they should be replaced by not selective schools. But from where i lived, grammar schools held all of the top positions in the league tables in my county/borough/town. All of the other schools in the area, comprehensives, were a dire alternative in terms of education and school life(regular riots/fights/bullying/drug problems). And, it has been shown that overall, grammar schools are a better learning environment and produce better results. My school was so good that people were trying to get their children in there rather than private schools, because we were better and we were free. Labour MPs who had abolished grammar schools were even trying to send they children there, and children from all over London were traveling to go there, rather than the city academies(which are severely underachieving).
If the local comprehensives were better than the grammars, i would have gone there, but they weren't. We were told as we collected our grades that we were the next generation or doctors, vets, lawyers, teachers, etc. The same could not be said for the other local schools.
Grammars aren't unfair, if you have the ability to get in, no matter what class, you can get in. The same can be said for universities. At my school i had people from all classes. And streaming schools, is in effect the same as creating selective grammar schools. And streaming a mixed school is a logistical nightmare. One school a friend went to had 6 different maths sets!