If your child had a gift for music, then you might send her to a school which excels musically.
If your child had a talent for sport, you might send him to an academy which excels at sport, one where he can really focus and develop in the area in which he is better than his peers.
And so on....!
So, if your child is intelligent, academically gifted... Why is it bad to say you would send her to a selective school where she can study along with other bright students?
If it's OK to separate children according to ability in sport or music or drama or technology, and send them to specialist schools which excel in these areas - why is it a different story if their talent with their academic ability?