I am a supporter of grammar schools, as long as they sit alongside other specialist schools of equivalent quality. There are schools which specilaise in sport for those children who excel at sport, there are schools that specialise in art/drama/music for the children who excel in those subjects, there are specialist language schools, specialist maths/computing schools. Why shouldn't there also be schools that specialise in the sort of rigorous academic education that some children excel at? In whatever activity you are doing, being surrounded by like-minded people of similiar ability helps you to up your game. If the ability is football or dance, no one has an issue about training those kids together. It's only for academic ability where some people have an issue. I really don't think that the problem is grammar schools themselves, it's that in some places, where there is a grammar system the other school options are simply poor.
In my (grammar) area, if you don't go to a grammar school the choice of other schools is excellent in theory; there's a specialist sports school, a language school, a performing arts school, a maths/computing school, a science/tech school plus the grammar. But in practice, two of these schools were in special measures and only one is 'outstanding'. So there is a big fight to get into the grammar schools and lots of children are tutored. But parents wouldn't feel they needed to do that if the other schools on offer were also good schools where kids could get a decect education whilst following their specialist interest. Funnily enough, the most popular school in the town isn't actually the grammar - it's a huge comprehensive with a grammar stream. Kids can move in and out of the grammar stream depending on how they are doing - it's a great model. But unless you are in catchment, the only way to get in is to go for the grammar stream (by sitting the 11+) or the schools own specialist entry test.
Will stop now as I've waffled long enough!