Big data is a dangerous part of this equation. Even when data appears to be anonymized, bringing multiple sources together can defeat that.
In a recent issue of Technology Review there was a long article about big data's role in the last US election. (It's not a party specific issue, but the article centered on the Obama camp because they had a much larger data operation this election).
You may think that your presidental vote is confidential, but the analysts are quite certain that they had identified virtually every voter who voted for Obama in '08 by amalgamating vast quantities of demographic data. On particular thing they did was purchase anonymized user info from cable companies and used external data to match those users to actual addresses and phone numbers. It got scientifically down to the point where the particular phone message one got from the phone bank was based on things like what show you watch and what was on your Tivo (you thought that was private?)
I don't know how we can stop this juggernaut, but it's out there.
-- FORTRAN manual for Xerox Computers --