What's wrong with grammar schools?

There's been a lot of criticism of Theresa May's intention to re-introduce grammar schools in the false hope of making everyone 'equal', but why?

Every kid is different with different abilities and the socialist dream of dumbing down education in order to make everyone inclusive is holding back kids with talent who need to be stretched to develop their potential.

I never passed the 11 plus but I do not resent other kids who did and had the talent to go on to a grammar school. The fact is that you cannot 'Nanny State' people into achieving educational success if they are not commited themselves and the idea that we should all live in a society that does not discriminate in terms of ambition and ability is ludicrous.