Not an ignorant question, but a reasonable one. I think the skeptics believe that society overall does not yet understand the tradeoff. And I agree with them there. I think on a deeper level, people are creeped out that data paints such a deterministic picture of our lives. Sure, I leave home the same time every day, and I leave work about the same time every day. That Google knows where I live and work without me ever explicitly saying shouldn't be a surprise, but not everyone enjoys seeing how their daily lives are so easily circumscribed, even with just passively-collected data.