I just finished reading the NYT best-seller In the Garden of Beasts: Love, Terror, and an American Family in Hitler's Berlin [1]. It made me think that, notwithstanding Godwin's Law [2], citizens should continue to be mindful of what can happen in a 'civilized' society.
[1] http://www.amazon.com/Garden-Beasts-Terror-American-Hitlers/... (not an affiliate link).
My plan to deal with this is to keep extremely aware of the political evolution where I live and to make sure that if it looks like such a regime is about to take power, I'm on the other side of the world with my family when that happens.
What's your plan?
If you don't want "the next Hitler" you need your political system to be designed to avoid allowing "him" to happen. Communism largely failed as a system because it consistently brought out the worst dictators in each country and put them on top. Having all this data in one place has no historical precedent. It is only smart to at least consider the worst case, given the potential damage.
If you don't like the Hitler analogy, then consider something close to home:
What would the Taliban have done with all this data on their people? The answer seems pretty obvious.
If the above scenario sounds unrealistic to you, that's right. It is unrealistic, just like the one you painted.
I'd rather not tell Google everything about myself but I'm honestly shocked that such extreme examples are being used to argue against the idea. By invoking Nazi analogies to make your point, you're actually doing a disservice to your argument. The instinct of my irrational mind is to think: well if it needs another Hitler to make it really scary, then I can probably ignore it.