Ignoring the arrogance, "If you have nothing to hide" isn't a valid question because everyone has something to hide. People have curtains and doors for good reasons, and everyone expects a certain amount of privacy in their lives -- but they don't realise how much they care about it until after they get screwed.

Oh, and it's not a slippery slope fallacy if we literally are headed towards 1984. Not even Orwell thought that social graphs would allow for automated analysis. The NSA doesn't need tele-screens when they have Facebook.