You’d have a point if there was any evidence that these specialist schools are producing better overall results for their students. There is no such evidence. There is however strong evidence that ghetto-ising the residual schools is doing real damage to the students there, entrenching disadvantage and raising the costs to society of the rising inequality that results. There is a case for specialist schools or at least classes for children with special needs, or for children of various ethnic communities. But the trend under Tomorrow’s Schools of “affluent flight” shows no benefit and plenty of costs.
As for charter schools, they could easily be accommodated within the state system – there is no need for them to sit outside.