Social media utilized for Presidential Election

Social media seems to have changed US Presidential Election substantially.

Now volunteers for both Obama and Romney campaigns are trying to influence the voting habits very efficiently: they utilize social media such as Facebook to obtain detailed knowledge of voters' lives and thus to decide target voters.

It seems to me the violation of privacy rights. Or is it just one of the strategies to win the election..?

http://www.nytimes.com/2012/10/14/us/politics/campaigns-mine-personal-lives-to-get-out-vote.html?_r=1&pagewanted=1&hp