Hydroponics certainly has its place in urban settings and I think that more and more urbanites ought to consider how to feed themselves. In that circumstance it has value. But it is water intensive and that won't suit a lot of locales and it does necessitate power sources (could be done with solar in the right climes) and therefore infrastructure that doesn't exist in Third World countries (who need these solutions right away...organics is a solution for everywhere (and repeated tilling is not part of sustainable organic culture; in NOFA we teach no-till systems as the best practice...)
We need to embrace our connection to the rest of the biota and a good place to do that is the soil. We can certainly find ways to work around soil, but I do not trust man's ability to replace every nuance that soil biologies bring to the table (as we have been doing for a hundred years) because, let's face it, the track record is bad. The Lancet's report of last year (on a decade plus long study) makes it very clear that raising your plant foodstuffs in organic soils raises nutrient density by an average of 25 to 30% with as high as 100% increases in root vegetables. I am no expert in hydroponics but do know a good deal about soil biologies and I would be interested to see a Soil Food Web biological assay on rock wool and nutrient solution. I'd bet the ranch and all the livestock that the soil is more fully active, in total biomass, total active bacteria, total active fungii, and most importantly, and I can't stress this enough, protozoal counts both numerical and by species. Microbial grazing by the higher level predators (amoebae, cilliates and flagellates) is where the poop loop starts and where nutrient etching from parent material begins, and to think that we could replicate those natural systems is hubris (and how we got in trouble in the first place).
Hydroponics has a role to play in places where access to soil is limited (urban settings, outer space, your closet in your college dorm room) but it is not now, nor should it ever be, a substitute for growing in soil. We have fooled ourselves for too long that we can do better than Nature, and it is biting our collective heinie in a list of ways already given here. Working within the natural framework gives us many benefits, and just as importantly, gives benefit to the rest of the biota at the same time. It is a system I can teach a farmer in Lagos or Vietnam or Iowa, and it works everywhere, with free, simple, inputs you can find in any country, no matter how rich or poor, with no need for complicated infrastructure. THAT is the kind of gardening and agriculture I can embrace as saving the planet...