Ok, so we bus all the poor kids to the better area comp, and all the wealthy kids to the poor area comp. What then?
More social mobility due to lack of selection according to what area you can afford to buy a house in.
At least with the grammar system bright children from very poor backgrounds can and do get into good schools. Either we want selective schools or we do not. If we do not, it has to be more than just getting rid of those that decide on academic ability.
Let us not have a comprehensive system where those in middle class areas pretend they are all for equality because they are sending their children to middle class comps.