I'm sorry but that's just not true! It may be where you are, but here we only have selective education and (in my town), the secondaries historically have been what they say 'secondary'.
There are a few places that have better secondaries in our county, but I cannot afford to live in them. Incidentally the secondaries get better funding for SEN than the grammars do.
My children would never have had the opportunity to 'mix' with the children they have/do if the grammar school system didn't exist, their friends were/are far more affluent than us (I'm disabled and can't work, DH is a bus driver, when DS was at school I was a single parent).
I'm not totally condemning the secondaries, I went to one ffs, a bloody awful one, and went to university, through sheer damned hard work. But the culture in these schools is one with a lot of disruption (chairs thrown at teachers/doors, etc), bad behaviour that isn't controlled, children being noisy and disturbing classes.
When I went to university it was in spite of my secondary school, not because of it. I think the same applies across the board, most of those who go to the secondaries and do really well have managed to keep their nose down and work.
I'm not totally in favour of grammars though, in spite of what I said above. I have to be living here, as the top students are creamed off (and no parent of an academically able student would duck out of the 11+, as it doesn't happen, so we are not in the same situation as areas with comprehensives).
A good comprehensive that catered for both the top and bottom, that allowed children to flourish, would of course be preferable.
I still state that I never had either of my DC tutored, as I said I simply couldn't afford it.